What does Hebrews 9:19 mean?
Blood is an important aspect of both the old and new covenants. In the old covenant, animal blood was used in order to temporarily cover the sins of the people. Since that blood could never fully pay for human sin, and had to be offered repeatedly, it was not God's ultimate plan for our salvation. Instead, God planned to use the human, perfect, once-for-all sacrifice of Jesus Christ in order to completely remove our sin. Recent verses have pointed out how blood was a necessary part of all of the old covenant rituals, and that those were always meant to be symbols of the new covenant.Verses 18 through 21 refer back to the very beginning of the old covenant, when Moses first introduced God's commands to the people. This is described in various places in the Old Testament, but most clearly in passages such as Exodus 24:6–8. The point being made is that this blood sacrifice was necessary, even from the very start of God's established laws for Israel. This leads to two ideas which will be made in upcoming verses. First, without bloodshed—sacrifice—forgiveness of sins is impossible. Second, the sacrifice of Jesus Christ not only fulfills this requirement, it does so perfectly and permanently.
Interestingly, Jesus used language similar to that of Moses when He introduced the new covenant (Matthew 26:28).