"Grace is of course the term we use for the principle operative in the gospel that was missing from the pre-Fall covenant. Properly defined, grace is not merely the bestowal of unmerited blessings, but God's blessing of man in spite of his demerits, in spite of his forfeiture of divine blessings. Clearly, we ought not apply the term grace to the pre-Fall situation, for neither the bestowal of blessings on Adam in the very process of creation nor the proposal to grant him additional blessings contemplated him as being in a guilty state of demerit. Yet this is what Fuller and company are driven to do as they argue for a continuum between the pre-Fall and the redemptive covenants. Only by thus using the term grace (obviously in a different sense) for the pre-Fall covenant can they becloud the big, plain contrast that actually exists between the two covenants (cf. Rom. 4:4).
Not grace, but simple justice, was the governing principle in the pre-Fall covenant; hence, it is traditionally called the covenant of works. God is just, and his justice is present in all he does. That is true of gospel administrations, too, for the foundation of the gift of grace is Christ's satisfaction of divine justice. If you are looking for an element of continuity running through pre-Fall and redemptive covenants (without obliterating the contrast between them), there it is—not grace, but justice. Recognizing that God's covenant with Adam was one of simple justice, covenant theology holds that Adam's obedience in the probation would have been the performing of a meritorious deed by which he earned the covenanted blessings" (Meredith G. Kline, Covenant Theology Under Attack, italics original).