In Reformed theology distinctions are quite important. There’s a distinction between the law and the gospel, between justification and sanctification, and between the covenant of works and covenant of grace (just to name a few). Here is how Herman Witsius explained the difference between the latter:
Here we are to observe a remarkable difference between the promises of the covenant of works, and those of the covenant of grace. The same eternal life is promised in both, which can be but one, consisting in the communion and enjoyment of God; but it is promised in a manner quite different in the one from what it is in the other.
In the covenant of works God promised life to man, on condition of perfect obedience; but he did not promise to produce or effect this obedience in man.
In the covenant of grace, he not only promises life eternal, but also at the same time faith and repentance, and perseverance in holiness, without which life cannot be attained, and which being granted, life cannot but be obtained. And even in this sense it may be said – that the covenant of which Christ is the Mediator is “more excellent, and established on better promises” (Heb. 8:6), because it does not depend on any uncertain condition, but is founded on the suretyship and actual satisfaction of Christ – does infallibly secure salvation to the believer, and as certainly promise faith to the elect.
Shane Lems
Hammond, WI
The Reformed Reader Blog 