Maybe you don't know, but God forgave sins before Christ.
Leviticus 4:2 “Speak to the sons of Israel, saying, ‘If a person sins unintentionally in any of the things which the LORD has commanded not to be done, and commits any of them..."(keep reading in your Bible)...4:35b "the priest shall make atonement for him in regard to his sin which he has committed, and he will be forgiven."
Was God fooling people? Was God not forgiving? May it never be! As Paul says in this typical rabbinic way of saying NO.
The problem of the system of sacrifices of the Law of Moses was that not all sins could be forgiven (only some), also intentional sinning was not covered. Paul, who had a deep understanding of the Law, realized that also the unforgivable sins became forgivable through the unique and eternal sacrifice of Christ is the cross. This is the Good News that Paul spread to the world.