Remember that Psalm 110 promised that God would send the special “Priest forever.” Hebrews 7 shows us that Priest. He is Jesus Christ! Jesus came from the family line of Judah and King David. But the Law of Moses was very strict about such matters. It said that its priests should come only from the family line of Levi and Aaron. How could Jesus have become our High Priest when He did not belong to the right family? Remember that it was God’s prophet who foretold that the Christ would come from Judah and David (Genesis 49:10; Psalm 89). It was also God’s prophet who said that this Christ would be “Priest forever” (Psalm 110). Therefore God must have planned some change. God planned a change of law, so that the King from Judah and David could become Priest. This conclusion is exactly what we find in Hebrews 7:12.
For when there is a change in the priesthood, there is necessarily a change in the law as well.
Hebrews 7:18 goes on to say that
”a former commandment is set aside.”
ERV: The old rule is now ended.