Jamieson, Fausset and Brown on 1 John 4:13

13. Hereby--"Herein." The token vouchsafed to us of God's dwelling (Greek, "abide") in us, though we see Him not, is this, that He hath given us "of His Spirit" (1Jo 3:24). Where the Spirit of God is, there God is. One Spirit dwells in the Church: each believer receives a measure "of" that Spirit in the proportion God thinks fit. Love is His first-fruit (Ga 5:22). In Jesus alone the Spirit dwelt without measure (Joh 3:34).