Jesus gave this powerful prayer to St. Faustina when He said, "I desire that you know more profoundly the love that burns in My Heart for souls, and you will understand this when you meditate upon My Passion...When you say this prayer, with a contrite heart and with faith on behalf of some sinner, I will give him the grace of conversion. This is the prayer:
O Blood and Water, which gushed forth from the Heart of Jesus, as a fount of mercy for us, I trust in You." (Diary 186-187)
Jesus also asked her to "Make a novena for the Holy Father's intention. It should consist of thirty-three acts; that is, repetition that many times of the short prayer - which I taught you - to The Divine Mercy." (Diary 341)
What a great blessing to have access to this powerful Prayer of Conversion Jesus taught St Faustina Himself.