Fesko begins chapter 4 by stating:
Foundational to any understanding of the doctrine of justification is the work of Jesus Christ, his life, death and resurrection and its application in justification, or redemption accomplished and applied. One cannot begin, however, with the work of Christ. Paul calls Christ the eschatological Adam (1 Cor. 15:45); additionally, Paul states that Adam is a type of the one to come (Rom. 5:14). The connection between the two Adams means that one must begin with the work of the first Adam before one can appreciate and understand the work of the last Adam…The (Westminster) divines write: “The first covenant made with man was a covenant of works, wherein life was promised to Adam; and in him to his posterity, upon condition of perfect and personal obedience” (WCF 7.2) (p107)
Fesko spends some time arguing that Genesis 1-3 provides ample evidence that Adam was in a covenant with God, despite absence of the word itself. For instance, the creation narrative mentions nothing about a covenant when God creates day and night. Yet in Jeremiah 33:20-21 we read, “If you can break my covenant with the day and my covenant with the night, so that day and night will not come at their appointed time, then also my covenant with David my servant may be broken, so that he shall not have a son to reign on his throne, and my covenant with the Levitical priests my ministers.” (ESV) Further evidence is marshalled, including the presence of God’s hovering Spirit:
In other covenantal contexts, the Holy Spirit is present as a witness to God’s covenantal activity: the exodus, baptism of Christ, and the consummation (p113)
After gathering evidence from Genesis 6:18, Hosea 6:7 and Romans 5:12-19, Fesko moves on to discuss the substance of the covenant of works. Interestingly, Fesko sees Adam as an archetypal Levite and the Garden as an archetypal temple. Inside the garden, there was order, outside disorder. Adam’s work was:
(1) multiply the image of God through procreation; (2) fill the earth with the image of God and expand the garden-temple to fill the earth – to bring the garden-order to the earth where there was no order – to subdue the earth; and (3) expand his vice regency throughout the whole earth by having men, made in God’s image, rule over the entire creation. (p124)
The Sabbath rest was a pointer to the fact that Adam’s state in the garden was not to be permanent and that, had Adam fulfilled the obligations of the covenant, he would have eaten of the tree of life and entered into a glorified state.
Fesko takes issue with critics of the term ‘covenant of works’ (including John Murray and anachronistically John Calvin) and sides with John Owen who maintain the need of the doctrine to protect the absolute necessity of Christ’s saving work.
Further, maintaining that works could justify Adam before the fall necessitates that works are totally excluded from justification after the fall. The only one who could be justified by works is Christ himself, who fulfilled Adam’s creation mandate. He was justified by works so that we could be justified by grace. How so?
Well, it's clear from Romans 5:12 that Adam represented not only himself but also all who were ‘in him’; Adam’s guilt was imputed to his descendants. Therefore, in like manner, the righteousness of Christ is imputed to his descendants. More on this in chapter 5.