In 1 John 4:20 John makes the point that Jesus had previously made in Matthew 22, which is that a true love for God will evidence itself in a love for others. In fact, John says, if we say we love God but fail in our duty to love our brothers and sister in Christ we show ourselves to be liars. What does it look like to love one another? Well in John 13:34 we see that it ought to look like the way Jesus has loved us. Jesus served us, he’s shown grace to us, he forgives us, and he sacrifices for us. This is the type of love we are called to demonstrate to one another and when we do so we show the world that we belong to Jesus and we show the world how deeply Jesus loves us.