6 “I write unto you, young men.” There are sons, are fathers, are young men: sons, because begotten; fathers, because they acknowledge the Beginning; why young men? “Because you have overcome the wicked one.” In the sons, birth: in the fathers, antiquity: in the young men, strength. If the wicked one is “overcome” by the young men, he fights with us. Fights, but not conquers. Wherefore? Because we are strong, or because He is strong in us who in the hands of the persecutors was found weak? He has made us strong, who resisted not His persecutors. “For He was crucified of weakness, but He lives by the power of God.”
7. “I write unto you, children.” Whence children? “Because you have known the Father. I write unto you fathers:” he enforces this, and repeats, “Because you have known Him that is from the beginning.” Remember that you are fathers: if you forget “Him that is from the beginning,” you have lost your fatherhood. “I write unto you, young men.” Again and again consider that you are young men: fight, that you may overcome: overcome, that you may be crowned: be lowly, that you fall not in the fight. “I write unto you, young men, because you are strong, and the word of God abides in you, and you have overcome the wicked one.”
Source: Homilies on the First Epistle of John (New Advent)