The Better Covenant Guarantor

The writer of Hebrews explains in more detail why it is that Christ is the better hope as high priest in comparison to the OT priests. That is because, unlike the OT priests, God swore an oath that Christ would be high priest forever (Psalm 110:4).

But why did God swear an oath on behalf of Christ's high priesthood and for the OT priests? Because Christ alone would be able to bring God's people to a state of pure holiness. Therefore, because Christ is able, unlike the OT priests, He is called the guarantor of a "better covenant", one that will surely transform God's people into a state of holiness.