Shalom,
God never gave any command that He required to be obeyed in order to become justified, but rather the one and only way that there has ever been to become justified is by faith, and by the same faith we are required to be careful to live in obedience to all of God's commands. Abraham was justified by faith, by the same faith he lived in obedience to all of God's commands, and God had no need to provide an alternative and unobtainable means of becoming justified by works when a perfectly good means of becoming justified by faith was already in place. According to John 8:56, Abraham saw Messiah's day and was glad, so the people who were justified in the OT were looked forward in faith to the promise of a redeemer just as we look backward in faith.
Take a scenario where someone owed you more money that they could ever repay, so you decide to forgive their debt. It wouldn't be a simple as just wiping the books clean because you would still be out the money they owed you, so in order to forgive their debt, you would essentially need to pay their debt for them in their place. The wages of Lawlessness is death, so that is the debt we owe, and in order for God to forgive us, He would need pay our debt for us in our place, and this is why it was necessary for Messiah to give himself to redeem us from all Lawlessness. We do not need to sacrifice Messiah, but rather he gave up his life on his own accord. I hadn't considered the angle where they needed to offer a sacrifice for their sin ignorance for crucifying Messiah, but I think you are reading too much into his words on the cross, especially if we would need to offer him as a sacrifice for the sin of offering him as a sacrifice. Also, Leviticus 4:27-29 does not stipulate that we will be justified by obeying that command, but rather if by faith we are careful to obey all God's commands, then it will be righteousness for us.