Set on him (επ' αυτω). Resting upon (επ) with locative rather than εις, looking to, Acts 24:15. That is upon Christ (Brooke), upon God (D. Smith), upon God in Christ (Westcott).

Purifieth himself (αγνιζε εαυτον). Present active indicative of αγνιζω, old verb, from αγνος (pure from contamination), used of ceremonial purifications (John 11:55; Acts 21:24; Acts 21:26 as in Exodus 19:10) and then of personal internal cleansing of heart (James 4:8), soul (1 Peter 1:22), self (here). Cf. Philippians 2:12 the work of both God and man.

As he is pure (καθως εκεινος αγνος εστιν). As in 1 John 2:6; 1 John 3:9 εκεινος (emphatic demonstrative) refers to Christ. Christ can be termed αγνος "in virtue of the perfection of his humanity" (Westcott). Our destiny is to be conformed to the image of God in Christ (Romans 8:29).