No man hath seen God at any time. If we love one another, God dwelleth in us, and his love is perfected in us. God, whom no man hath seen at any time, appoints His children the visible recipients of our outward kindness, flowing from love to Himself, 'whom not having seen, we love' (1 Peter 1:8: cf. note, 1 John 4:11; 1 John 4:19-20). Thus, 1 John 4:12 explains why, instead (in 1 John 4:11) of saying, 'If God so loved us, we ought also to love God,' he said, "We ought also to love one another."
If we love one another, God dwelleth in us - for God is love. It must have been from Him dwelling in us that we drew the love we bear to the brethren (1 John 4:8; 1 John 4:16: discussed, 1 John 4:13-16).
His love - rather, 'love of (i:e., to) Him,' evinced by love to His representatives, our brethren.
Is perfected in us. (Discussed, 1 John 4:17-19.) Compare 1 John 2:5, "Is perfected;" i:e., attains its maturity.