Remember that the audience of this letter is Jewish believers, and this period of time may have been difficult to hold onto their newfound Christian faith. Before Christianity was familiar, it was new and it was probably very tempting to go back to an old set of beliefs, because it may have felt safer. The writer of Hebrews has already been doing the work of establishing who Jesus was and is, and now he puts it directly into a familiar Jewish context: what Moses was, Jesus is greater than. Moses symbolizes the law, so that’s the meaning here. What the law started, Jesus finished. We can still trust that today.