Is the Covenant of Grace a unilateral (or unconditional) covenant of promise (as maintained by theologians such as Dr. Michael Horton in such works as “God of Promise,” now retitled “Introducing Covenant Theology“)? Or is that merely a Lutheran innovation?
No less than the Reformed Orthodox theologian Francis Turretin (1623-87), at least, argued for a unilateral formulation of the Covenant of Grace:
Not without reason did the Holy Spirit wish to designate the covenant of grace under the name of “promise,” because it rests entirely upon the divine promise. In this it wonderfully differs, not only from all human covenants (which consist of a mutual obligation and stipulation of the parties), but from the covenant of works (which although it also had its own promise on the part of God to the doers and so was founded on the goodness of God, still it required obedience on the part of man that it might be put into execution). But here God wished the whole of this covenant to depend upon his promise, not only with regard to the reward promised by him, but also with regard to the duty demanded from us. Thus God performs here not only his own part, but also ours; and if the covenant is given for the happiness of only the one party, it is guarded and fulfilled by the fidelity of only one party. Hence not only God’s blessings fall under the promise, but also man’s duty; not only the end, but also the means and conditions leading us to it. – Institutes of Elenctic Theology, 12.1.11.
And although the promise of the covenant is conditionally proposed and applied to individuals, it does not follow that the promise itself depends upon man’s will and so is not absolute. That conditional promise is a consectary [consequence] of an absolute promise and it is thus commanded as the duty of man that it may be produced at the same time and at once in the elect as the gift of God. – Institutes of Elenctic Theology, 12.6.3
Thus, at least for Turretin, it is not wrong to conceive of the Covenant of Grace as a unilateral (or unconditional) arraignment. Although faith is certainly the condition apart from which the promise is void, even this faith is a gift of God and secured by God as part of the promise.