Genesis 17:6-7

"And I will make thee exceedingly fruitful, and I will make nations of thee, and kings shall come out of thee. And I will establish my covenant between me and thee and thy seed after thee throughout their generations for an everlasting covenant, to be a God unto thee and to thy seed after thee."

"For an everlasting covenant ..." The great purpose of this covenant was the delivery of the Messiah to redeem all mankind, and that aspect of it was indeed eternal. However, the land promise, mentioned a little later, was contingent, absolutely, upon Israel's keeping the terms of the covenant and continuing to walk before God and submitting to His government. (See comments under Genesis 17:8, below.)