Answer
"Covenant of works" refers to an administration in the early chapters of Genesis in which God came to Adam and told him in Genesis chapter 2 not to eat of the fruit of the Tree of Knowledge of Good and Evil, for on the day that he ate of it he would surely die. The covenant of works held out to Adam life and death. If Adam disobeyed God then death would be the result. Had Adam obeyed God, continued in obedience to God, which he didn't, then confirmed life would have been the result. And Adam was a representative person, as Paul teaches in Romans 5 and 1 Corinthians 15. And what that means is that when Adam obeyed or disobeyed, and in this case he disobeyed, he did so as the representative of his posterity, so that when he sinned and death came into the world, his sin was reckoned to his posterity and so death to them.
Answer by Dr. Guy Waters
Dr. Guy Waters is the James M. Baird, Jr. Professor of New Testament at Reformed Theological Seminary.