{And he in him} (kai autos en aut(9369)). That is "God abides
in him" as in  4:15 . We abide in God and God abides in us
through the Holy Spirit ( Joh 14:10,17,23  17:21 ). "Therefore
let God be a home to thee, and be thou the home of God: abide in
God, and let God abide in thee" (Bede). {By the Spirit} (ek tou
pneumatos). It is thus (by the Holy Spirit, first mention in
this Epistle and "Holy" not used with "Spirit" in this Epistle or
the Apocalypse) that we know that God abides in us. {Which}
(hou). Ablative case by attraction from accusative ho (object
of ed(936b)en) to agree with pneumatos as often, though not
always. It is a pity that the grammatical gender (which) is
retained here in the English instead of "whom," as it should be.