Actually, Dispensationalism is nothing but simply believing the explicitly stated promises God made, not only to Abraham, but to Isaac, to Jacob to the ancient nation of Israel, to the two sub-divisions of that ancient nation, Judah and Ephraim, to the twelve tribes of Israel, to the lands of Israel and Judea, to the city of Jerusalem, and to numerous specific individuals. All of these promises were explicitly made in plain words. And if God could righteously break even one of them, He could fully as righteously break the promises He made to us.
When anyone denies the future restoration of the ancient nation of Israel to her ancient homeland and to her God, they deny the ONLY basis for our own faith, which is the absolute reliability of God to keep every promise He ever made.