How do we know that we love God's children? When we love God and follow his commands.
This is my command to you: love one another.
We can be sure that we do know him if we follow his commands.
But those who follow God's word have his love totally fill their minds. This is how we know that we live in him.
The reason we know that we have changed from death to life is because we love our Christian brothers and sisters. Anyone who doesn't love remains dead.
This is the command he gave to us: those who love God love their brothers and sisters too.