5 Do ye imagine, brethren, that they whose instruments re-echoed yesterday, are not angry with our fastings? But let us not be angry with them, but let us fast for them. For the Lord our God who sits in us has said, He has Himself commanded us to pray for our enemies, to pray for them that persecute us: and as the Church does this, the persecutors are almost extinct....The drunken man does not offend himself, but he offends the sober man. Show me a man who is at last happy in God, lives gravely, sighs for that everlasting peace which God has promised him; and see that when he has seen a man dancing to an instrument, he is more grieved for his madness, than for a man who is in a frenzy from a fever.
If then we know their evils, considering that we also have been freed from those very evils, let us grieve for them; and if we grieve for them, let us pray for them; and that we may be heard, let us fast for them. For we do not keep our own fasts in their holidays. Different are the fasts which we celebrate through the days of the approaching Passover, through different seasons which are fixed for us in Christ: but through their holidays we fast for this reason, that when they are rejoicing, we may groan for them.
For by their joy they excite our grief, and cause us to remember how wretched they are as yet. But since we see many freed thence, where we also have been, we ought not to despair even of them. And if they are still enraged, let us pray; and if still a particle of earth that has remained behind be stirred up against us, let us continue in lamentation for them, that to them also God may grant understanding, and that with us they may hear those words, in which we are at this moment rejoicing.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)