Historian Thomas Cahill says that in ancient times humanity believed we were caught in an endless cycle: birth, struggle, and death. It never ended and never altered in its turning. No one lived with an expectation that there was something in the future.
God's call to Abraham and Sarah broke that vicious cycle. God did not call Abraham to be content in his insignificance. Instead, He called Abraham to break out of the meaningless cycle. He called Abraham to be a part of His plan for rescuing a dying world. So, says Cahill, God's call to Abraham was a radical break in the history of the world. People began to think in terms of a linear worldview instead of a circular one. In other words, there was a future and there could be hope for something different in that future.