God abides in people who confess that Jesus is the Son of God, and they abide in God. This testifies to God's love and to the fact that God is love.
The notion that God is love is one of the most important and influential teachings in 1 John. It follows from the metaphor God is light. We walk in the light when we abide in God by the power of the Spirit through faith in Jesus Christ, and in this way we love one another, love God, and properly love ourselves. This is how we know and walk in God, for God is love. Love for God and a proper love for self should lead us to love our sisters and brothers in Christ. Anyone who says "I love God" but hates his sisters and brothers is a liar.
13 By this we know that we abide in him and he in us, because he has given us of his Spirit. 14And we have seen and do testify that the Father has sent his Son as the Saviour of the world. 15God abides in those who confess that Jesus is the Son of God, and they abide in God. 16So we have known and believe the love that God has for us.
God is love, and those who abide in love abide in God, and God abides in them. 17Love has been perfected among us in this: that we may have boldness on the day of judgement, because as he is, so are we in this world. 18There is no fear in love, but perfect love casts out fear; for fear has to do with punishment, and whoever fears has not reached perfection in love. 19We love* because he first loved us. 20Those who say, I love God, and hate their brothers or sisters,* are liars; for those who do not love a brother or sister* whom they have seen, cannot love God whom they have not seen. 21The commandment we have from him is this: those who love God must love their brothers and sisters* also.
New Revised Standard Version Bible: Anglicized Edition, copyright © 1989, 1995 National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved worldwide. http://nrsvbibles.org