And he is the atoning sacrifice{"atoning sacrifice" is from the Greek "hilasmos," an appeasing, propitiating, or the means of appeasement or propitiation-- the sacrifice that turns away God's wrath because of our sin.} for our sins, and not for ours only, but also for the whole world.

 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. 