From Works of Love, Ch. 4, “Our Duty to Love Those We See,” ht MS:
Christ’s love for Peter was so boundless that in loving Peter he accomplished loving the person one sees. He did not say, “Peter must change first and become another man before I can love him again.” No, just the opposite, he said, “Peter is Peter, and I love him; love, if anything, will help him to become another man.” Therefore he did not break off the friendship in order perhaps to renew it again when Peter had become another man. No, he preserved the friendship unchanged and in this very way helped Peter to become another man. Do you think that Peter would have been won again without this faithful friendship of Christ? But it is so easy to be a friend when it means nothing more than requiring something in particular from the friend, and if he does not respond to the demand, then to let the friendship go — until it perhaps is renewed when he responds to the demand. Is this the relationship of friendship? Who is closer to helping an erring one than the person who calls himself a friend, even if the offence is committed against the friend! But the friend withdraws and says (yes, as if a third person were talking): when he has turned over a new leaf, he can perhaps become my friend again. And we human beings are not far from regarding even such behavior as highminded. But truly, one is far from being able to say of such a friend that in loving he loves the person he sees.