8 “With them that hated peace, I was peaceful”. But howsoever ye may hear, most beloved brethren, you will not be able to prove how truly ye sing, unless you have begun to do that which you sing. How much soever I say this, in whatsoever ways I may expound it, in whatsoever words I may turn it, it enters not into the heart of him in whom its operation is not. Begin to act, and see what we speak. Then tears flow forth at each word, then the Psalm is sung, and the heart does what is sung in the Psalm...Who are they who hate peace?
They who tear asunder unity. For had they not hated peace, they would have abode in unity. But they separated themselves, forsooth on this account, that they might be righteous, that they might not have the ungodly mixed with them. These words are either ours or theirs: decide whose. The Catholic Church says, Unity must not be lost, the Church of God must not be cut off. God will judge afterwards of the wicked and the good...This we also say: Love ye peace, love ye Christ. For if they love peace, they love Christ.
When therefore we say, Love ye peace, we say this, Love ye Christ. Wherefore? For the Apostle says of Christ, “He is our peace, who has made both one.” If Christ is therefore peace, because He has made both one: why have ye made two of one? How then are you peace-makers, if, when Christ makes one of two, you make two of one? But since we say these things, we are peace-makers with them that hate peace; and yet they who hate peace, when we spoke to them, made war on us for nought.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)