This is made clear in Romans 11;24 where Paul points out that the Christian Church is grafted into the Jewish rots of the Christian faith.
Paul states, “And even those others [the fallen branches, Jews], if they do not persist in [clinging to] their unbelief, will be grafted in, for God has the power to graft them in again. For if you have been cut from what is by nature a wild olive tree, and against nature grafted into a cultivated olive tree, how much easier will it be to graft these natural [branches] back on [the original parent stock of] their own olive tree”. Romans 11:23-24 AMP
The heart of the Old Covenant is the Temple Sacrifice on the Day of Atonement. This will be discussed in detail below. The point is that Jesus did not abandon completely the Temple Sacrifice Model, known as the Old Covenant, but replaced it with a New Covenant based on the same model, becoming Himself the Lamb of God, slain before the foundation of the world.