“This new system was established with a solemn oath. Aaron’s descendants became priests without such an oath, but there was an oath regarding Jesus. For God said to him,
‘The Lord has taken an oath and will not break his vow:
‘You are a priest forever.’
Because of this oath, Jesus is the one who guarantees this better covenant with God.
There were many priests under the old system, for death prevented them from remaining in office. But because Jesus lives forever, his priesthood lasts forever. Therefore he is able, once and forever, to save those who come to God through him. He lives forever to intercede with God on their behalf. He is the kind of high priest we need because he is holy and blameless, unstained by sin. He has been set apart from sinners and has been given the highest place of honor in heaven. Unlike those other high priests, he does not need to offer sacrifices every day. They did this for their own sins first and then for the sins of the people. But Jesus did this once for all when he offered himself as the sacrifice for the people’s sins. The law appointed high priests who were limited by human weakness. But after the law was given, God appointed his Son with an oath, and his Son has been made the perfect High Priest forever.”
The Bible is often much more than it seems. In today’s passage the author of Hebrews quotes Psalm 110, which we mentioned at the start of chapter 7 as one of the few passages that mentions Melchizedek. It’s not clear whether King David, the author of Psalm 110, knew that his little song was a profound and prophetic statement. It’s confusing right from the start when it says, “The Lord said to my Lord…” Why are there two Lords? How can that be? Perhaps David did realize that he was seeing something about the coming Messiah.
Because of Psalm 110, we see a bit of God’s relationship within himself — the Father, Son, and Holy Spirit. He’s talking to Jesus and taking an oath which will be in effect for all of eternity. This captures the supernatural moment that Jesus was appointed as the eternal and perfect High Priest. He is the only one that had the power to offer himself as a sacrifice once for all.

God doesn’t forget about his promises. He doesn’t take an oath and then change his mind. Verse 22 says that Jesus is our guarantee of our covenant with God. Let’s think about it this way — when a person is trying to buy a house, they have to submit an offer. They can do that with a simple letter, or they can include an approval letter from a bank. Even better is the offer that includes proof of sufficient cash to make the entire purchase. The money is the guarantee that the offer is actually good. I could put a whole bunch of offers on million dollar homes, but I have no proof to offer that I have that money to give (because I don’t!). An offer is only as good as the proof that you can really follow through. Jesus is God’s proof that he will follow through and rescue his people — he still hasn’t given up yet!