Brethren, according to man I speak. Nevertheless, concerning a covenant of man, having been ratified, no one sets it aside or adds to it, Galatians 3:15.
Even by the standards of men, once a covenant has been ratified, it cannot be added to or annulled. In light of this, how much more are the covenants made by God assured by His Word?
Since a covenant cannot be modified, it follows that the covenants God gave to Abraham concerning his descendants may not be given to another. For example, in Genesis 15:18–21, God made a covenant with Abram to give his descendants the land. This is for his literal children. Later, in Genesis 17:7–8, God made a second covenant with Abraham, after changing his name. This covenant relates to a land promise for his descendants in eternity. The second covenant does not supersede nor modify the first covenant.
Furthermore, neither of these covenants are impacted by the Mosaic Law, which was given to Israel to display to all that through the flesh no man can be justified before God, Romans 3:20. Christ came to fulfill the Mosaic law, not abolish it, Matthew 5:17. In order to remove the covenant of law, so that He can place Israel under a new covenant in the Millennial Kingdom, as the testator of the covenant, He had to die to release them, Hebrews 9:16.
Understanding this, we see that when God makes a covenant, that covenant cannot be annulled or added to. Therefore, God did not give the covenants of Israel to the Church, for the grace believer is given a better covenant based on better promises with a heavenly hope, Hebrews 8:6 and Colossians 1:5.