5 Mark what comes next: “Blessed are the merciful, for they shall obtain mercy.” Do this, and so shall it be done to you; deal so with others, that God may so deal with you. For you are at once in abundance and in want— in abundance of temporal things, in want of things eternal. The man whom you hear is a beggar, and you are yourself God's beggar. Petition is made to you, and you make your petition. As you have dealt with your petitioner, so shall God deal with His. You are at once full and empty; fill the empty with your fullness, that your emptiness may be filled with the fullness of God.
Source: Sermons on Selected Lessons of the New Testament (New Advent)