Abideth (menei). Present active indicative, continues in the light and so does not interrupt the light by hating his brother.
Occasion of stumbling (skandalon). See note on Mat 13:41; and note on Mat 16:23 for this interesting word. It is a stumbling block or trap either in the way of others (its usual sense), as in Mat 18:7, or in one’s own way, as is true of proskoptō in Joh 11:9 and in 1Jo 2:11 here. But, as Westcott argues, John may very well have the usual meaning here and the other in 1Jo 2:11.