The Law and the priesthood were a shadow of the reality. They were not the fullness of God's purposes, but they weren't useless, either. They pointed the way; the Hebrews author did not want any to be so enraptured with the shadow so as to turn away from its reality and fulfillment.

How do we find relief and strength in Jesus' sacrifice for sin? Why would we eagerly await Jesus' return?

The New and Living Way | Episode 24 | Hebrews 9:23-10:4

It was necessary therefore that the copies of the things in the heavens should be cleansed with these; but the heavenly things themselves with better sacrifices than these. For Christ entered not into a holy place made with hands, like in pattern to the true; but into heaven itself, now to appear before the face of God for us: nor yet that he should offer himself often, as the high priest entereth into the holy place year by year with blood not his own; else must he often have suffered since the foundation of the world: but now once at the end of the ages hath he been manifested to put away sin by the sacrifice of himself.

And inasmuch as it is appointed unto men once to die, and after this cometh judgment; so Christ also, having been once offered to bear the sins of many, shall appear a second time, apart from sin, to them that wait for him, unto salvation.

For the law having a shadow of the good things to come, not the very image of the things, can never with the same sacrifices year by year, which they offer continually, make perfect them that draw nigh. Else would they not have ceased to be offered? because the worshippers, having been once cleansed, would have had no more consciousness of sins. But in those sacrifices there is a remembrance made of sins year by year. For it is impossible that the blood of bulls and goats should take away sins.