Yeshua died not only for the sins that were committed after His death, but also for the sins committed prior to His death. He died not just for the sins of New Testament saints, but also for the sins of Old Testament saints. God could have judged the Old Testament saints immediately , but He deferred their judgment until the cross. Then that judgment fell upon the Messiah as their substitute as well as the substitute for New Testament believers. In that way, their sins were removed.
This is taught by Acts 17:30: The times of ignorance therefore God overlooked; but now he commands men that they should all everywhere repent: ...
He made the same point in Romans 3:25: ... whom God set forth to be a propitiation, through faith, in his blood, to show his righteousness because of the passing over of the sins done aforetime, in the forbearance of God; ... Again, he pointed out that the sins committed before the death of the Messiah could have been judged immediately , but they were deferred, temporarily overlooked or “passed over,” until the death of the Messiah as their substitute.
In Hebrews 10:4, the writer said: For it is impossible that the blood of bulls and goats should take away sins.
Animal sacrifice did not and could not remove the sins of the Old Testament saints; it merely covered them temporarily . Once the Messiah died, only then were their sins removed as well.