By this we know that we remain in Him, and He in us: He has given us of His Spirit.
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" (Jo1 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 (Gal 5:22).
Love descends from heaven itself, it is God's nature and the fruit of His Spirit. Whoever loves with genuine holy affection is born of God and knows Him truly. But whoever loves not, knows not God; such a soul shows by its very coldness that true knowledge of the divine nature has no dwelling place within it.
AI summary
Commenting on 1 John 4:7-13
Hereby know we that we dwell in him, and he in us,.... That there is a communion between God and us, and a communication of his love and grace to us, and an exercise of grace upon him; for God dwells in his people by his Spirit and grace, and they dwell in him by the exercise of faith and love upon him: and this...