The kind of compassion referred to here [in the Beatitudes] is not simply giving alms to the poor or orphan or widow. This kind of compassion is often found even among those who hardly know God. But that person is truly compassioniate who shows compassion even to his own enemy and treats the enemy well. For it is written, “Love your enemies, and treat well those who hate you.” Remember that God too sends his rain and asks his sun to rise not only over the grateful but also over the ungrateful. So Jesus calls us to “be compassionate, just as your Father is compassionate.” Such a person is truly blessed, for if in fact he hasn’t sinned, which is difficult for us all, God’s grace helps him along in increasing his sense of justice. So he prays, “Forgive me my debts, just as I too forgive my debtors.”

–Anonymous, Incomplete Works on Matthew, Homily 9