They went out from us, but they didn't belong to us; for if they had belonged to us, they would have continued with us. But they left, that they might be revealed that none of them belong to us.

 So, then, John means that we are assured of forgiveness because we know the character of Jesus Christ. We know that in him we see God. We see in him sacrificial love and patient mercy; therefore we know that God is like that; and, therefore. we can be sure that there is forgiveness for us. 