Jesus urged Sister Faustina to write and speak of His mercy, as she noted in her Diary: Tell souls where they are to look for solace; that is, in the Tribunal of Mercy. There the greatest miracles take place [and] are incessantly repeated. To avail oneself of this miracle, it is not necessary to go on a great pilgrimage or to carry out some external ceremony; it suffices to come with faith to the feet of My representative and to reveal to him one's misery, and the miracle of Divine Mercy will be fully demonstrated. Were a soul like a decaying corpse so that from a human standpoint, there would be no [hope of] restoration and everything would already be lost, it is not so with God. The miracle of Divine Mercy restores that soul in full (Diary, 1448).
This revelation without doubt belongs to the series of those which pertain to St. Faustina's mission, that is, her labor for the purpose of furthering devotion to The Divine Mercy; but it also pertains to the devotion itself.
In this revelation, Jesus called sacramental confession "the tribunal of mercy," and declared: ...it suffices to come WITH FAITH to the feet of My representative [that is, a priest] and to reveal to him one's misery. The faith He referred to is the theological virtue that St. Paul indicates has an intimate connection with hope, expressing by that fact strong confidence in God's merciful goodness (Rom. 5:1-5).
By speaking about such confidence in connection with the Sacrament of Reconciliation within the context of the devotion to The Divine Mercy, and by referring three times to the result of the two as "this miracle of Divine Mercy," Jesus incorporated sacramental confession into the practices of the devotion that render special honor to His mercy, so that not only confession in preparation for the Feast of Mercy but every act of sacramental confession is considered an integral part of this devotion. By the same token this devotion, this practice according to the Lord's will, constitutes an authentic part of the Christian life.