Brethren, I write no new commandment unto you, but an old commandment which ye had from the beginning. The old commandment is the word which ye have heard from the beginning. Brethren, I write no new commandment - There seems a contradiction between this and the next verse. But the apostle appears to speak, not so much of any difference in the essence of the precept itself, as in reference to the degrees of light and grace belonging to the Mosaic and Christian dispensations. It was ever the command of God that men should receive his light, walk by that light, and love him and one another. But this commandment was renewed by Christ with much latitude and spirituality of meaning; and also with much additional light to see its extent, and grace to observe it. It may therefore be called the Old commandment, which was from the beginning; and also a New commandment revealed afresh and illustrated by Christ, with the important addition to the meaning of Thou shalt love thy neighbor as thyself, ye shall love the brethren so as to lay down your lives for each other. See the note on John 13:34.
Instead of αδελφοι, brethren, ABC, thirteen others, with both the Syriac, Erpen's Arabic, Coptic, Sahidic, Armenian, Slavonic, and Vulgate, with several of the fathers, have αγαπητοι, beloved. This is without doubt the true reading.