If you dropped an object into the middle of the vast ocean you would know, with deep certainty, that this object would get wet. The immensity of the ocean would consume it. So it is with the Mercy of God. It is immense and infinite. Therefore, if you trust in His Mercy, you can have a deep certainty that you will obtain it (See Diary #420).
Do you trust that God will bestow His infinite Mercy upon you? The goal is to be certain of this. We do not arrive at this certainty because of our own goodness; rather, we arrive at it as a result of the unfathomable and infinite Mercy of the Most Holy Trinity.
Lord, I love You and I desire to trust in Your perfect Mercy to the point that there is no doubt in my mind and heart that You will bestow this precious gift. Help me to trust in Your Mercy because of Your infinite goodness. Purify me of all doubt, dear Lord, and help me to trust You more. Jesus, I trust in You.