By this we know that we abide in him and he in us, because he has given us of his Spirit.
As the Spirit of truth is known by doctrine (thus spirits are to be tried), it is known by love likewise; and so here follows a strong fervent exhortation to holy Christian love: Beloved, let us love one another, Jo1 4:7.
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...
Verse 13. Hereby know we that we dwell in him. Here is another, or an additional evidence of it. Because he hath given us of his Spirit. He has imparted the influences of that Spirit to our souls, producing "love, joy, peace, long-suffering, gentleness, goodness, faith," etc., .