And he that keepeth his commandments dwelleth in him, and he in him. And hereby we know that he abideth in us, by the Spirit which he hath given us.
Dwelleth in him. The Believer dwelleth in Christ.
And he in him - Christ in the believer. Reciprocity. 'The key-note of the letter, abide in Him, with which the former part concluded' (1 John 2:28) (Alford).
Hereby - `herein we (believers) know that He abideth in us, namely, from (the presence in us of) the Spirit.' This prepares, by mention of the true Spirit, for the transition to false "spirits," 1 John 4:1-6; after which he returns again to love.