[O]ur editors have summarized Turretin as teaching that “the form of the Mosaic covenant was the covenant of works, but its substance was the covenant of grace” (12). This muddles Turretin’s otherwise careful distinctions regarding the administration of the covenant of grace under Moses, and oversimplifies his rather complex formulation. It is true that Turretin argues that the Mosaic administration contained a restatement of a “form of the covenant of works” to remind Israel of the broken covenant of works and to lead them to Christ (2:263). But Turretin later clarifies that by “form of the covenant of works,” he is referencing “the law in itself” apart from the Mosaic covenant (2:269). This he distinguishes from “the Mosaic covenant itself, in which the law was enacted” (ibid.). This administration included not only this “legal relation” but also an “evangelical relation,” which was “sweeter” in that it led them to Christ (2:227). Thus, Turretin calls this administration a “mixture of both the law and the Gospel” (2:263). As he says elsewhere: “And thus in sweet harmony the law and the gospel meet together in this covenant. The law is not administered without the gospel, nor is the gospel without the law. So that it is as it were a legal-gospel and an evangelical-law; a gospel full of obedience and a law full of faith” (2:268). In short, our editors summary of Turretin’s view of the Mosaic covenant is at best severely truncated, and at worst, misleading. It fails to grapple with Turretin’s own stated definitions, and oversimplifies Turretin’s complex (though very precise) views.
I don't post this comment to endorse it (I haven't carefully enough studied Turretin's relevant writings to form a conclusion), but simply as an interesting point worthy of further consideration. Turretin's careful distinctions are one of his principle advantages and following them is critically important in understanding his writing.