Augustine of Hippo : "In this we know that we are in Him, if in Him we be perfected." Perfected in love, he calls them: what is perfection of love? To love even enemies, and love them for this end, that they may be brethren. For not a carnal love ought ours to be. To wish a man temporal weal, is good; but though that fail, let the soul be safe. Dost thou wish life to any that is thy friend? Thou doest well. Dost thou rejoice at the death of thine enemy? Thou doest ill. But haply both to thy friend the life thou wishest him is not for his good, and to thine enemy the death thou rejoicest at hath been for his good. It is uncertain whether this present life be profitable to any man or unprofitable: but the life which is with God without doubt is profitable. So love thine enemies as to wish them to become thy brethren; so love thine enemies as that they may be called into thy fellowship. For so loved He who, hanging on the cross, said, "Father, forgive them, for they know not what they do." For he did not say, Father let them live long, me indeed they kill, but let them live. He was casting out from them the death which is for ever and ever, by His most merciful prayer, and by His most surpassing might. — Ten Homilies on 1 John 1 Bede : But whoever keeps His word, etc. Therefore, truly the one who keeps God's commandments and proves by his love has true knowledge of God. For to know God is to love Him. For whoever does not love Him clearly shows that he does not know how lovable He is. And he has not learned to taste and see how sweet and pleasant the Lord is, who does not strive continuously to please Him through intent devotion. — Commentary on the Catholic Epistles Bede : By this we know that we are in Him, etc. That is, through excessive love, even to pray for enemies, just as He did, saying, "Father, forgive them" (Luke XXIII). Also, to despise all the favorable aspects of the world with a strong mind, to willingly endure insults and reproaches, just as He said: "If anyone desires to come after Me, let him deny himself, and take up his cross, and follow Me" (Luke IX). — Commentary on the Catholic Epistles Clement of Alexandria ((as quoted by Cassiodorus)) : "But whoever keeps His word, in him verily is the love of God perfected: hereby know we that we are in Him," - by faith and love. — From the Latin Translation of Cassiodorus Didymus the Blind : The person who really loves God keeps his commandments and by so doing realizes that he knows the love of God. Our obedience results in his love. — COMMENTARY ON 1 JOHN Hilary of Arles : Love sustains all those who try to put God's commandments into practice. — INTRODUCTORY COMMENTARY ON 1 JOHN Oecumenius : "But whoever keeps his word, in him truly the love of God is perfected. By this we know that we are in him." Therefore, whoever knows God is also known by Him, either having become a partner with God and united with God; and in this, the love of God is evident, through which love he will have the perfection that is in God, and by this, he will judge his closeness to God. For perfect love is indeed exhibited through works. — Commentary on 1 John