The law is only an unclear picture of the good things coming in the future; it is not the real thing. The people under the law offer the same sacrifices every year, but these sacrifices can never make perfect those who come near to worship God.
The work they do as priests is only a copy and a shadow of what is in heaven. This is why God warned Moses when he was ready to build the Holy Tent: “Be very careful to make everything by the plan I showed you on the mountain.”