Oecumenius

By this we know that we love the children of God, when we love God and keep his commandments. And John adds this persuasion: that whoever loves the one who created him loves also the one who is born of him. Then he uses a change of discourse and says that love for brothers or the children of God confirms love for Him who created. For John previously said: "he who loves God must love his brother also. (1 Jn. …

Commentary on 1 John ↗

Augustine of Hippo

"In this we know that we love the sons of God, in that we love God." And how? Are not the sons of God one thing, God Himself another? But he that loves God, loves His precepts. And what are the precepts of God? "A new commandment give I unto you, that ye love one another." Let none excuse himself by another love, for another love; so and so only is it with this love: as the love itself is compacted in one, so all that hang by it doth it make one, and as fire melts them down into one. …

Ten Homilies on 1 John 10 ↗

Bede

In this we know that we love the children of God, etc. Therefore, he alone is proven to love his neighbor rightly who is known to burn with the love of the Creator. And lest anyone deceive himself about the love of the Creator, professing that he loves by word alone, after having said: In this we know that we love the children of God, when we love God, he added, and we keep His commandments.

Commentary on the Catholic Epistles ↗