Adam and Christ
In the covenant of grace God does not grant us anything beyond what he would have given Adam had he been faithful. The covenant of grace does not differ from the covenant of works in its eschatological goal, only in the road taken: Adam’s obedience versus Christ’s.12 In the simplest of terms, there was an eschatology before the fall; eschatology is older than soteriology. Justification is older than salvation.13 Adam’s justification was supposed to be on the basis of his obedience, but Christ secured his justification by his obedience. Christ’s obedience is then the foundation for our justification. Adam’s justification was by obedience, but now in a fallen world our justification can only be by faith in Christ—by trusting in the obedience of the last Adam. Justification is therefore either by works or by faith alone in Jesus’s works.
John Fesko. The Giver of Life: The Biblical Doctrine of the Holy Spirit and Salvation (p. 179). Lexham Press. Kindle Edition.