24.What is true, therefore?

The Law of Moses cannot invalidate a contract, a covenant, that was ratified by God hundreds of years previously. Paul is informing the Gentiles of Galatia that it is not the Gospel of Christ that is the newcomer but the Law of Moses. The Gospel came first.

The Law, coming hundreds of years after the Gospel, cannot set aside the Divine promises made to Abraham and to his Seed by the Lord God of Heaven. The promises referred to here are those concerning Christ and the blessings that will come to the earth through Him.