In a word—Jesus!
The former regulation is set aside because it was weak and useless (for the law made nothing perfect), and a better hope is introduced, by which we draw near to God. And it was not without an oath! Others became priests without any oath, but he became a priest with an oath when God said to him: “The Lord has sworn and will not change his mind: 'You are a priest forever'”. Because of this oath, Jesus has become the guarantor of a better covenant (Hebrews 7:18-22).
The book of Hebrews was written to make this one point — the New Covenant is better than the Old in every way.
The reason is simple. The New Covenant totally rests on the shoulders of Jesus.
His once for all sacrifice.
His eternal priesthood.
His indestructible life.
As Hebrews 7:22 states, “This makes Jesus the guarantor of a better covenant.”
His resurrected life in you guarantees that every promise, every provision of the New Covenant becomes a reality in your life.
No longer do you have to rely on human effort. You can trust the one who loved you and gave himself for you.
So what makes the New better than the Old?
In a word — Jesus.
Let these words go deep in your soul: “Therefore he is able to save completely those who come to God through him, because he always lives to intercede for them. Such a high priest truly meets our need – one who is holy, blameless, pure, set apart from sinners, exalted above the heavens” (Hebrews 7:25, 26).
Your priest, Jesus Christ, has saved you completely.