The fact that we are called “Christians” proves it. The name “Christian” was not applied to the people of God until Acts 11:26 in Antioch. The disciples of Jesus were called Christians. Even in that one verse you see a shift in recognition–no longer “disciples” but Christians.
God’s people were called different things throughout the thousands of years of history. Psalms calls them “godly” a few times. They are called “righteous” a number of times. Of course, once Israel was established as a nation they are called “Israel,” “my people,” “children,” and various other terms.
The fact that we call ourselves Christians today is a relatively new thing. If you call yourself a Christian you are at the same time admitting that there are differences in God’s relationship to His people over the years, which is called dispensationalism, whether you want to admit it or not.