When we hear the words "committed in ignorance" the immediate temptation is to think that this limits the atonement of Jesus to only the sins that we commit without being aware of them… but nothing could be further from the truth. There is application to prohibit the presumptuous sin from being covered… (no, pre-asking for forgiveness allowed) but I think that the main issue here is that ALL of our sin is committed in ignorance. In almost all the other places where the atonement is addressed it is specifically given for ALL the sins of the people.