Adam's Role in the Garden of Eden

I don't understand Covenant Theology so I am reading an introduction named, A Sacred Bond: Covenant Theology Explored by Michael G. Brown and Zach Keele. Genesis 3 is a pivotal chapter for covenant theologians. The authors explain Adam's role in the garden of Eden in the following quote. This explanation is new to me.

That the first Adam failed in his responsibility to carry out judgment on the serpent is further elucidated in verses 23-24, which tell us that the Lord relieved Adam of his priestly duty of protecting the holiness of the garden and gave it to the cherubim with the flaming sword. In Genesis 2:15 we are told that “the LORD God took the man and put him in the garden of Eden to work and keep it.” In order to reach the goal of the Tree of Life, Adam was to remain obedient in these covenant responsibilities. He was not only to take care of the garden as a gardener but also protect it as a guardian. Eden was a holy temple and sanctuary to the Lord. Protecting it from defilement was part of his priestly responsibility to the Lord. Thus, he failed in the covenant of works even before he ate of the forbidden tree. He failed when he allowed his wife to enter into league with the devil. At that very point, he should have exercised his priestly authority and executed judgment on the Serpent. Consequently, “the LORD God sent him out from the garden of Eden to work ground from which he was taken. He drove out the man, and at the east of the garden of Eden he placed the cherubim and a flaming sword that turned every way to guard the way to the tree of life” (Gen. 3:23-24). Fallen Adam could continue in his responsibility to “till” or “tend” the earth (now cursed and bearing thorns) as an everyday function for life. But his holy responsibility of “guarding” the garden was taken from him and given to the cherubim as he failed in his priestly duty to protect Eden from defilement. If God’s elect were to reach to goal of the Tree of Life, God would need to send a new Adam to exercise judgment on the Serpent, which is precisely what he promises in Genesis 3:15: “He will bruise your head.” (p. 62-63)