Beloved, if God loved us this much, we also ought to love one another.
In context
9This is how the love of God was revealed among us: God sent his one and only Son into the world, so that we might live through him. 10This is love: not that we loved God, but that he loved us and sent his Son as the atoning sacrifice for our sins. 11Beloved, if God loved us this much, we also ought to love one another. 12No one has ever seen God. But if we love one another, God remains in us, and his love is made complete in us. 13This is how we know that we remain in him and he in us: he has given us of his Spirit.
