I have not written to you because you don't know the truth, but because you know it, and because no lie is of the truth.

 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. 