3 “In this is His love perfected in us, that we may have boldness in the day of judgment.” Why shall we have boldness? “Because as He is are we also in this world.” You have heard the ground of your boldness: “Because as He is,” says the apostle, “are we also in this world.” Does he not seem to have said something impossible? For is it possible for man to be as God? I have already expounded to you that “as” is not always said of equality, but is said of a certain resemblance.
For how do you say, As I have ears, so has my image? Is it quite so? And yet you say“so, as.” If then we were made after God's image, why are we not so as God? Not unto equality, but relatively to our measure. Whence then are we given boldness in the day of judgment? “Because as He is, are we also in this world.” We must refer this to the same charity, and understand what is meant. The Lord in the Gospel says, “If you love them that love you, what reward shall you have?
Do not the publicans this?” Then what would He have us do? “But I say unto you, Love your enemies, and pray for them that persecute you.” If then He bids us love our enemies, whence brings He an example to set before us? From God Himself: for He says, “That ye may be the children of your Father which is in heaven.” How does God this? He loves His enemies, “Who makes His sun to rise upon the good and the bad, and rains upon the just and the unjust.” If this then be the perfection unto which God invites us, that we love our enemies as He loved His; this is our boldness in the day of judgment, that “as He is, so are we also in this world:” because, as He loves His enemies in making His sun to rise upon good and bad, and in sending rain upon the just and unjust, so we, since we cannot bestow upon them sun and rain, bestow upon them our tears when we pray for them.
Source: Homilies on the First Epistle of John (New Advent)