Their sins were forgiven, but not cleared. Sins were forgiven, but not washed away. If they did not offer sacrifices for their trespasses, they were cut off from God. The best these sacrifices could do is land them up in Abraham's bosom upon death.
Exodus 34
4 And he hewed two tables of stone like unto the first; and Moses rose up early in the morning, and went up unto mount Sinai, as the Lord had commanded him, and took in his hand the two tables of stone.
5 And the Lord descended in the cloud, and stood with him there, and proclaimed the name of the Lord.
6 And the Lord passed by before him, and proclaimed, The Lord, The Lord God, merciful and gracious, longsuffering, and abundant in goodness and truth,
7 Keeping mercy for thousands, forgiving iniquity and transgression and sin, and that will by no means clear the guilty; visiting the iniquity of the fathers upon the children, and upon the children's children, unto the third and to the fourth generation.