Trust and deed
The essence of the devotion to God's Mercy is trust in God's goodness. Without this trust, the service cannot exist - because worshiping God's Mercy is nothing else than trusting Him.
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).
God's mercy never leaves a person. It accompanies on all roads of life – always ready to help. However, only trust in His Mercy opens and moves the human heart to a fruitful reception of the grace of the good God, allowing Him to operate freely in the soul.
He who trusts in My mercy will not perish, for all his affairs are mine (Diary 723). The soul that trusts in My mercy is most fortunate, because I Myself take care of it (Dz. 1273). No soul that has called upon My mercy has been disappointed or brought to shame. I delight particularly in a soul which has placed its trust in My goodness (Diary 1541).
Trust is the human response that precedes the reception of God's Merciful Love. Knowing mercy is nothing else but trust Him. Trust in the ineffable goodness of God allows us to drink from the fountain of God's Mercy.
I demand from you deeds of mercy, – said Lord Jesus to Sister Faustina – which are to arise out of love for Me. 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 (Diary 742).
Trust in God's mercy should be accompanied by the practice of charity expressed by deed, word and prayer. The Lord Jesus wants us to have done, during the day, at least one such act of mercy, while having the pure intention of pleasing only Him. From this source of pure love of God flows our love of neighbor. This intention of the selfless love of our Savior completely differentiates Christian mercy from any other charity that lacks the reality of Jesus' love.