And hateth his brother (κα τον αδελφον αυτου μισων). Sharp contrast between the love just described and hate. The only way to walk in the light (1 John 1:7) is to have fellowship with God who is light (1 John 1:3; 1 John 1:5). So the claim to be in the light is nullified by hating a brother.

Even until now (εως αρτ). Up till this moment. In spite of the increasing light and his own boast he is in the dark.