A Puritan Theology: Doctrine for Life in a Year:
Having discussed the similarities between the two covenants [of works and of grace], [Patrick] Gillespie [1617-1617] turns his attention to the differences between the two covenants, “which are manifold and substantial.” While both covenants are designed to advance the glory of God, they nevertheless differ in their special ends.
The first covenant was made with man in innocency; he was to persevere in the garden through his obedience. The second covenant was made with sinful man in order to restore him to happiness. The original happiness that Adam possessed is far inferior to the happiness that saints in the covenant of grace will enjoy.
The Puritans commonly asserted that saints enjoy far greater privileges in the covenant of grace than Adam did in Eden. Not only Gillespie, but Thomas Goodwin in his exposition of the covenant of works has a decided stress on the superior state of believers in the covenant of grace, who enjoy supernatural graces as opposed to Adam’s natural dues in the covenant of nature.
In Gillespie’s view, those in the second covenant have a certainty of perseverance that Adam never had. A significant support for Gillespie’s position is that the mystical and spiritual union with Christ, promising and securing the blessings He procured for His people, given in the covenant of grace, is much superior to the mere moral union (that is, a union of affections) that Adam had with God. Moreover, the believer possesses God and Christ, who dwells in the elect (John 14:20; Gal. 2:20), a privilege Adam did not have.
(A Puritan Theology, p. 29-30)