The Essence of the Devotion to the Divine Mercy 
The mission of the Blessed Sr. Faustina gives birth to new forms of devotion to the Divine Mercy. Its foundation is the attitude of trust in God and mercy toward one's neighbors. 
Trust in this devotion is understood as inner attitude toward God which is expressed in the fulfillment of His will. Such an attitude is made up of a number of virtues, the most important of which is: faith, hope and love, as well as humility and contrition. Trust grows out of getting to know the secret of God's merciful love for man. It is not an emotional attitude, a feeling or an intellectual act which recognizes God's revelation as the ultimate truth, but it is man's lifetime attitude toward merciful God which is expressed in the fulfillment of His will. The words: Jesus, I Trust in You - which can be seen underneath the image of the Divine Mercy, are man's most appropriate response to his getting to know the mystery of the Divine mercy and his experiencing of God's mercy in his own life. 
Trust constitutes the foundation of the devotion to the Divine Mercy to such an extent that without it, one cannot talk about the cult of the Divine Mercy the way the Lord Jesus wished it. Every form of the devotion described by the Blessed Sr. Faustina becomes an authentic act of worship of the Divine Mercy and will bring the desired fruits (among others, the fulfillment of Jesus' promises), if it flows out of the attitude of inner trust in God. Trust is such an essential act of devotion to the Divine Mercy that even without the practice of other forms of the devotion, it assures the attainment of graces contained in the general promises which the Lord Jesus associeted with this devotion. The graces of My mercy are drawn by means of one vessel only, and that is - trust. The more a soul trusts, the more it will receive (Diary 1578). 
Mercy towards one's neighbors is the second, besides trust, essential element of this devotion. Through the Blessed Sr. Faustina, the Lord Jesus reminds us about the basic Christian duty: You are to show mercy to your neighbors always and everywhere. You must not shrink from this or try to excuse or absolve yourself from it. I am giving you three ways of exercising mercy toward your neighbor: the first - by deed, the second - by word, the third - by prayer; in these three degrees is contained the fullness of mercy, and it is an unquestionable proof of love for Me. By this means a soul glorifies and pays reverence to My mercy (Diary 742). In the private revelations to the Blessed Sr. Faustina the Lord Jesus expressed a desire, that those who worship Him should perform out of love for Him through deed, word or prayer at least one act of mercy toward their neighbors every day. He also explains that mercy for the soul is of greater merit and adds that one does not need material resources to implement it. Mercy may and should be practiced by every human individual. It is a requirement which is set forth in the Holy Gospel before all those who have been baptised. Thanks to this, the worship of the Divine Mercy, does not have a merely devotional character, but is a deeply experienced form of Christian life

The Image of the Divine Mercy 
The image of the Divine Mercy originates from the private vision that Sr. Faustina had in the cell of the Płock convent on February 22 1931. In the evening when I was in my cell, I saw the Lord Jesus clothed in a white garment. One hand was raised in the gesture of blessing, the other was touching the garment at the breast. From beneath the garment, slightly drawn aside at the breast, there were emanating two large rays, one red, the other pale (...) After a while, Jesus said to me: Paint an image according to the pattern you see, with the signature: "Jesus, I trust in You" (Diary 47). 
The image represents the crucified and risen Christ who brings man peace and salvation through remittance of sins and all the graces and gifts at the price of His passion. What is characteristic of the image are two rays: a red and a pale one. When asked about their meaning Jesus explained: The two rays denote Blood and Water. The pale ray stands for the Water which makes souls rightous. The red ray stands for the Blood which is the life of souls (Diary 299). Thus, the two rays denote above all the holy sacraments. Happy is the one who will dwell in their shelter, for the just hand of God shall not lay hold of him - said the Lord Jesus (Diary 299). Man's response to the above gifts of mercy is to be the attitude of trust. Hence in the inscription underneath the image, one is able to read the words: Jesus I Trust in You. The image representing God's mercy toward man is at the same time a sign which is to remind us about the evangelical summons to active love of one's neighbors. Thus, the cult of the image of Merciful Jesus consists in prayer of trust combined with deeds of mercy toward one's neighbors.
In the revelations of Blessed Sr. Faustina, the Lord Jesus attached a number of promises to the thus understood veneration of the image of the Divine Mercy. The soul that will venerate this image will not perish (Diary 48) - said the Lord, in this way promising salvation, as well as progress on the road to Christian perfection - a victory over the enemies of the soul, as well as the grace of a happy death (Diary 48). Yet the Lord Jesus did not limit His generosity to the above-mentioned specific graces, as He also said: I am offering people a vessel with which they are to keep coming for graces to the fountain of mercy. That vessel is this image with the signature: "Jesus, I trust in You" (Diary 327). By means of this Image I shall be granting many graces to souls (Diary 570 The first image of Merciful Jesus had been painted by Eugeniusz Kazimirowski in Vilno in the year 1934. It was executed under the direct supervision of Sr. Faustina. The image had first been exposed to the faithful for public veneration in the Shrine of Our Lady of Mercy in Ostra Brama on the first Sunday after Easter on 26-28 April 1935. Today this image is being venerated in the church of the Holy Spirit in Vilno. Yet, it was the image of Merciful Jesus painted by Adolf Hyła which the artist presented to the convent chapel in Cracow-Łagiewniki as a votive offering for the miraculous saving of his family from the war, that has become famous throughout the world. In this way, the words spoken by the Lord Jesus to Sr. Faustina during the first vision Sr. Faustina had in Płock, had become reality: I desire that this image be venerated, first in your chapel, and then throughout the world (Diary 47).
The Feast of the Divine Mercy 
I desire that the first Sunday after Easter be the Feast of Mercy (Diary 299) - the Lord Jesus said to Sr. Faustina. In the following years, Jesus returned to this demand in as many as 14 different apparitions, establishing very clearly the location of this Feast in the Church's liturgical calendar, and defining the reason and objective of its institution, the manner in which preparations for it and the celebration itself were to be conducted. 
Jesus explained why he wanted this Feast instituted: Souls perish in spite of My bitter passion ...I am giving them the last hope of salvation that is, the Feast of Mercy. If they will not adore My mercy, they will perish for eternity (Diary 965). The Feast is to be a day of special worship of God in the mystery of His mercy which is the source and motive of all His acts toward man, and particularly of the act of redemption. In accordance with God's will, it is also a day of special grace for all souls, and particulalrly for sinners who are most in need of God's mercy. The Feast of My Mercy - Jesus said - has issued forth from My very depths for the consolation of the whole world (Diary 1517). 
It is with this very day, and more precisely, with the Holy Communion received on this day after making a good confession, that the greatest of the Lord's promises is connected. We are referring here to the promise of complete remission of sins and punishment (Diary 300). Yet this grace is much more than just a plenary indulgence. A plenary indulgence entails merely the remission of temporal punishment, for sins committed, but it never amounts to the remission of the sins themselves. This grace is basically also greater than the grace of the six Sacraments, other than Baptism, since the remission of sins and punishment is the sacramental grace only of Holy Baptism. Whereas in the above promises, Jesus has attributed the power to remit sins and punishment to the Holy Communion received on the Feast of Mercy (...) Obviously, the Holy Communion must be received on this day not only in a state of grace, but all other basic conditions of the devotion to the Divine Mercy must be observed (Rev. I. Różycki).
The Lord Jesus did not limit His generosity to this single though so exceptional a grace, but promised to pour out a whole ocean of graces upon those souls who approach the fount of His mercy, as on that day all the divine floodgates through which graces flow are open (Diary 699). The greatness of this Feast consists among others in the fact that all people, even those who have only become converted on that day, may partake of all the graces Jesus has prepared for this Feast. The graces and benefits may be received by both the individuals and whole communities, providing they ask for them in a spirit of great trust. The preparation for this feast is to be a novena consisting of the recitation of the Divine Mercy Chaplet for nine days, beginning on Good Friday. Sr. Faustina's Diary also contains an example of a novena which Jesus dictated for her personal use indicating for whom she should pray. All Christians may likewise make this novena with fervor and piety. Whereas the novena consisting of the chaplet to the Divine Mercy should be looked upon as the most appropriate preparation to the Feast, in accordance with the wish of the Lord Jesus. The Feast as Jesus conceived of it holds forth the promise of every possible grace (Diary 796). s regards the manner in which the Feast is to be celebrated, Jesus wished that on that day the image of Mercy be given public veneration. He also wished that the priests should tell souls of the great and unfathomable mercy of God; the faithful should practice acts of mercy toward their neighbors and they should receive with trust the Sacrament of Reconciliation and the Holy Eucharist. The Divine Mercy had been worshipped spontaneously on the first Sunday after Easter already during the II World War. Officially, the Feast had first been instituted in the Cracow diocese by Franciszek Cardinal Macharski in his annual Pastoral Letter for Lent in the year 1985. In the subsequent years, the bishops of other Polish dioceses followed his example. In the year 1995 at the specific request of the Polish Episcopate, the Holy See issued a decree which permitted the celebration of this Feast in all Polish dioceses, provided the liturgical order for this day is preserved.

The Chaplet of the Divine Mercy 

Our Father..., Hail Mary..., the Apostles' Creed...,
On the large bead (one time):
"Eternal Father, I offer You the Body and Blood, Soul and Divinity of Your Dearly Beloved Son, Our Lord, Jesus Christ, in atonement for our sins and those of the whole world." 
On each small bead (ten times):
"For the sake of His sorrowful Passion, have mercy on us and on the whole world." 
Conclusion (three times):
"Holy God, Holy Mighty One, Holy Immortal One, have mercy on us and on the whole world." 

On September 13, 1935 Sr. Faustina had a vision in her cell of an angel coming to punish the world for its sins. When she saw this sign of God's anger, she started to beg the angel to hold off for a while yet, for the world to do penance. However, when she came before the Majesty of Holy Trinity, she did not dare repeat her plea. It was only when she felt the power of Jesus' grace in her soul that she started praying in the words that she heard from within, and saw that the punishment had been removed from the earth. On the next day, when she entered the chapel Jesus again gave her detailed instruction how this prayer was to be said, using the ordinary rosary beads. 
With the words of this prayer: I offer You the Body and Blood, Soul and Divinity, we are offering up to God the Father the Person of God the Son in His Divinity and His Humanity. While praying in this way we behave likewise during an act of offering, which is celebrated in the Eucharistic sacrifice. We can participate in the offering of Christ through the common priesthood of the People of God. By reciting the words of Your dearest Son - we refer to the love which God the Father has for his Son, and through Him for all the people. In this way, we are resorting to the strongest motive we can for God to hear our prayer. 
The words: for the sake of His sorrowful passion refer not only to the satisfaction Christ accomplished on the cross, but also they refer to the merciful love revealed the most in the passion of the Son, which God the Father bestows on man. Therefore by reciting the chaplet, we wish that the sorrowful passion of God's Son be not vain, but we want it to bring fruit in our life and in the lives of all people. 
In the chaplet we ask for mercy for us and for the whole world . The pronoun "us" denotes the person saying the prayer and those for whom he/she is or wishes to pray. Whereas the words the whole world stand for all the people alive on earth and the souls suffering in purgatory. 
In a dozen or so revelations the Lord Jesus showed the value and effectiveness of this prayer pointing out to the promises which are connected with it. It pleases me to grant souls everything they ask of Me when they say the chaplet (Diary 1541), if what you ask for is compatible with My will (Diary 1731). The will of God is an expression of His merciful love for man, so anything that is not compatible with it is either evil or harmful, and thus cannot be granted by the Heavenly Father. The specific promises concern the hour of death: the grace of happy and peaceful death. The grace in question will be received not only by those who recite the chaplet themselves, but also by the dying at whose deathbed other people say the chaplet. Priests will recommend it to sinners as their last hope of salvation. Even if there were a sinner most hardened, if he were to recite this chaplet only once, he would receive grace from My infinite mercy (Diary 687) - says the Lord Jesus. Thus the greatness of this promise rests in the fact that it is to be granted to any sinner who should recite the whole chaplet at least once, but in the spirit of devotion to the Divine Mercy that is in the attitude of trust, humility, and in sincere repentance for his sins. The recitation of the chaplet should not only be an outward act of inner trustfulness , but it should also be persistent. For Jesus promised that we would be able to obtain anything by saying this chaplet, but nowhere - except for the grace of good death - did He say that once was enough. 
Besides the exclamatory prayer: Jesus I Trust in You, the chaplet is the best known and most popular prayer to the Divine Mercy. It is recited in all corners of the world and has been translated even into some African dialects.

The Hour of Mercy
In October 1937 in Cracow the Lord Jesus said to Sister Faustina: At three o'clock, implore My mercy especially for sinners and, if only for a brief moment immerse yourself in My Passion, particularly in My abandonment at the moment of agony. This is the hour of great mercy for the whole world (Diary 1320). Such is the history of the origin of this form of worship of the Divine Mercy. A few months later, Jesus repeated His request defining precisely the aim of institiution of this form of cult, how to observe the Hour of Mercy, and mentioning what promises are connected with saying the prayer at this hour. He also defined the conditions which had to be met for prayers at this hour to be heard. 
The Hour of Mercy is a form of the cult in which we worship the moment of Christ's agony on the Cross (3 p.m.) when grace became available to the whole world and mercy triumphed over justice (Diary 1572). What is meant here by the "hour" is not a clock hour or 60 minutes of prayer, but saying a prayer at the moment when the clock strikes the third hour (Diary 1572), that is at the moment of Christ's agony on the Mount of Calvary. This form of worship of the cult of the Divine Mercy can be practiced not only on Good Friday, or on every Friday of the month, but everyday. It is a special time in the devotion to the Divine Mercy. 
At this hour the Lord Jesus wants us to meditate even though for a brief moment upon His sorrowful passion in which the mystery of His mercy is revealed in the fullest possible way. Getting to know this mystery leads to prayer of praise and thanksgiving, as well as begging for graces for the whole world, and especially for sinners, for at that moment mercy was opened wide for every soul ( Diary 1572). 
The Lord Jesus attaches the promise of all possible graces to the prayer at this special hour. In this hour, I will refuse nothing to the soul that makes a request of Me in virtue of My Passion (Diary 1320). In this hour you can obtain everything for yourself and for others for the asking (Diary 1572). At the same time, Jesus pointed out that there were three necessary conditions which had to be met for prayer at this hour to be heard: the prayer should be said at three o'clock in the afternoon, it was to be addressed to Jesus, and it was to refer to the values and merits of His Passion. Moreover, it should be added that the object of the prayer has to be in accordance with the will of God, and that the prayer should be trustful, persevering and combined with the practice of active love of one's neighbor, which is a condition of genuine devotion to the Divine Mercy. 
The Lord Jesus also gave Sr. Faustina some detailed advice relating to the ways in which she should pray at the Hour of Mercy: Try your best to make the Stations of the Cross in this hour, provided that your duties permit it; and if you are not able to make the Stations of the Cross, then at least step into the chapel for a moment and adore in the Blessed Sacrament, My Heart, which is full of mercy; and should you be unable to step into the chapel, immerse yourself in prayer, if only for a brief instant (Diary 1572). 
The Hour of Mercy is currently becoming a time of everyday prayer for the apostles of the Divine Mercy the world over. That is why, as if in a continual act of prayer, the faithful all over the world unite with Jesus dying on the Cross - and fulfilling His request - implore for God's mercy for the world and particularly for sinners

The Spreading of the Worship of Mery
Among the new forms of devotion to the Divine Mercy described by Sr. Faustina, one also finds the spreading of the worship of Mercy, as this form of devotion is also connected with the promises the Lord Jesus addressed to all those who undertake this devotional form. Jesus did not precisely define the ways of spreading the worship of Mercy, but He gave us a perfect example of such an apostolate in the life of Sr. Faustina. Thus, the worship of Mercy is primarily to be disseminated through a life in the spirit of total trust in God, that is the fulfillment of His will and mercy towards one's neighbors. Yet, one must not limit oneself to the above stipulations, as one should also proclaim by word the message of Mercy to the world and arouse trust and confidence in one's neighbors. On the pages of the Diary the Lord Jesus summons us many a time to spread the truth about God's merciful love for man, so that each and every one of us could take full advantage of the time and the gifts of mercy upon the earth thus attaining salvation. Oh, if sinners knew My mercy - the Lord confided in Sr. Faustina - they would not perish in such great numbers. Tell sinful souls not to be afraid to approach Me, speak to them of My great Mercy (Diary 1396).
Jesus attaches great importance to the above task, as He addresses special promises to those who perform it. Souls who spread the honor of My mercy I shield through their entire lives as a tender mother her infant, and at the hour of death I will not be a Judge for them, but the Merciful Savior (Diary 1075). Jesus addresses a special note of encouragement to priests ensuring them that hardened sinners will repent on hearing their words when they speak about My unfathomable mercy, about the compassion I have for them in My Heart (Diary 1521). In order to acquit oneself well of the above task, one has to primarily get to know the mystery of God's mercy, meditate upon it after prior analysis of the Holy Scriptures, the encyclical Dives in Misericordia, Sr. Faustina's Diary, as well as other books which have received the Imprimatur of the Church. Penetrating the mystery of the Divine Mercy in the act of creation, salvation and man's eternal unity with God, as well as noticing the operation of God's merciful love in one's personal life, gives rise to the attitude of trust and mercy, as well as a wish to spread this message to others.