The Law of Moses is like a shadow of the good things to come. This shadow isn't the good things themselves, because it cannot free people from sin by the sacrifices that are offered year after year.
The Law appoints priests who have weaknesses. But God's promise, which came later than the Law, appoints his Son. And he is the perfect high priest for ever.
But Christ was sinless, and he offered himself as an eternal and spiritual sacrifice to God. That's why his blood is much more powerful and makes our consciences clear. Now we can serve the living God and no longer do things that lead to death.