Jamieson, Fausset and Brown on 1 John 2:9-11

9-11. There is no mean between light and darkness, love and hatred, life and death, God and the world: wherever spiritual life is, however weak, there darkness and death no longer reign, and love supplants hatred; and Lu 9:50 holds good: wherever life is not, there death, darkness, the flesh, the world, and hatred, however glossed over and hidden from man's observation, prevail; and Lu 11:23 holds good. "Where love is not, there hatred is; for the heart cannot remain a void" [Bengel].

in the light--as his proper element.

his brother--his neighbor, and especially those of the Christian brotherhood. The very title "brother" is a reason why love should be exercised.

even until now--notwithstanding that "the true light already has begun to shine" (1Jo 2:8).