Well you cannot overcome what the Lord clearly said in His Word by the Holy Ghost thru His Apostle....
Hebrews 10:9
Then said he, Lo, I come to do thy will, O God. He taketh away the first, that he may establish the second.
Hebrews 7:12
For the priesthood being changed, there is made of necessity a change also of the law.
Didn't you read my post. I said the sacrifice was changed because Jesus replaced all animal sacrifices, Yet Jesus sacrifice is still working today, so therefore the necessity for a sacrificial Lamb is still necessary for all those who need salvation and that Law is still in practice. The priesthood was changed because the veil was rent asunder and Jesus became the high priest because we no longer need a mercy seat. Yet Jesus is the High Priest and that hasn't changed. Look, we got new wine flasks and new wine, but the need for a flask and wine are still necessary. Establishing in the old testament the greater things to come was absolutely and complexly necessary, but the old testament because God's word (Jesus) is in there is the establishment for a new, because the new was the propitiation once and for all time.
The old Testament dealt with Transgressions and Iniquities. Every year God would pass over their Transgressions with a first born, unblemished Lamb and the reason is because the Lamb was innocent of having brought sin in the world. Man could not find a first born Unblemished Son of man to be sacrificed for man. Even Isaac had to be rejected because he was born of the sin nature. So mans iniquities could never be removed, because iniquity is the condition in which man stood before God; in other words - CONDEMED. They all remained in the grave (not hell) until Jesus set the captives free even though their transgression were passed over.
The work of redemption on the cross (the new flask) removed all that, but greater, the whole issue of sin was pardoned. "I have cast your sins as far as the east is from the west". This is what the old established, and on that foundation and establishment came the new. God did all of that by His wisdom and He gets the Glory and all the praise. Moses had NOTHING to do with it except serve God as His messenger. GOD DID IT ALL.