God needs to take no oaths since His words are always reliable. So when He chooses to take one, it’s clearly a moment in history in which He wants us to know with absolute certainty that He will do what He’s said.
God’s oath
A change in the law
Hebrews continues to emphasise the need for a finer priest if we are to know God. God’s law, and the priests appointed under it, were a blessing to Israel. But they were weak, unable to save people
Help from others
Melchizedek was the priest-king of Salem (later Jerusalem) when Abraham was wandering the land.