Again, a new commandment I write unto you, which thing is true in him and in you: because the darkness is past, and the true light now shineth.
A new commandment. It was "old," in that Christians as such had heard it from the first; but "new" х kainee (G2537), not nea: new and different from the old legal precept], in that it was first clearly promulgated with Christianity: though the inner spirit of the law was love even to enemies, yet it was enveloped in some bitter precepts, which caused it to be temporarily almost unrecognized. Christianity first put love to brethren on the new and highest MOTIVE, instinctive love to Him who first loved us, constraining us to love all, even enemies, thereby walking in the steps of Him who loved us when enemies. So Jesus calls it "new," John 13:34-35: "Love one another, as I have loved you" (the new motive), John 15:12.
Which thing is true in him and in you. 'In Christ all things are always true, and were so from the beginning; but in Christ and in us conjointly the commandment (the love of brethren) is then true when we acknowledge the truth which is in Him, and have the same flourishing in us' (Bengel, Alford). Which thing (the fact that the commandment is a new one) is true in the case of Him and of you, because the darkness is passing away in the case of you, and the true light is now shining, and began to shine ever since He came into the world, bringing this commandment. I prefer, The new commandment finds its truth in its practical realization in the walk of Christians in union with Christ. Compare "verily," 1 John 2:5; John 4:42; John 6:55, "indeed." The repetition, "in Him and in you," not "in Him and you," implies that the love-commandment finds its realization separately: first "in Him," and then "in us," in so far as we now "also walk even as He walked;" yet it finds its realization also conjointly, by the two being united in one sentence, even as it is by the love-commandment having been first fulfilled in Him, that it is also now fulfilled in us, through His Spirit in us: cf. a similar case, John 20:17, "My Father and your Father:" by virtue of His being "My Father," He is also your Father.
Darkness is past - rather, as 1 John 2:17, 'is passing away.' It shall not be wholly "past" until "the Sun of righteousness" shall arise visibly: "the light is shining" already, though partially until the day bursts forth.