Were Old Testament Believers Motivated by Eternal Rewards?

Did Adam and Eve know about the doctrine of eternal rewards? What about subsequent generations? Enoch (generation seven)? Abraham (generation twenty)? Moses (generation twenty-six)? King David (generation thirty-four)? Various words are used in the OT to refer to the idea of rewards: reward, recompense, reap, and judgment are four of the most prominent. While it
