Seeing all the people were in ignorance. Literally, "because (sc. it happened) to the whole nation in ignorance." As the stranger was counted as of the nation for religious purposes, he shared both in its sin and in its forgiveness.
There is no record of this atonement ever having been made, although there was abundant occasion for it; it may well be that it was intended only to stand on record against the Jews, and to point them to the one true expiation for their national as well as for their particular transgressions.