Hebrews 10:1

Hebrews 10:1. For the law having a shadow of good things to come, and not the very image of the things, can never with those sacrifices which they offered year by year continually make the comers thereunto perfect.

This refers to the old ceremonial law, under which the Jews lived so long. They always had to go on, year after year, offering the same kind of sacrifices, because the work of atonement was never done perfectly; men were not cleansed or saved by it, so the process had to be constantly repeated.