Douglas Wilson found this gem from Turretin. It should settle the issue, but trust me, it will not.
“The Mosaic covenant may be viewed in two aspects: either according to the intention and design of God and in order to Christ; or separately and abstracted from him. In the latter way, it is really distinct from the covenant of grace because it coincides with the covenant of works and in this sense is called the letter that killeth and the ministration of condemnation, when its nature is spoken of (2 Cor. 3:6, 7). But it is unwarrantably abstracted here because it must always be considered with the intention of God, which was, not that man might have life from the law or as a sinner might be simply condemned, but that from a sense of his own misery and weakness he might fly for refuge to Christ…The law is said “to be not of faith” (Gal. 3:12), not as taken broadly and denoting the Mosaic economy, but strictly as taken for the moral law abstractly and apart from the promises of grace (as the legalists regarded it who sought life from it)” (2:267-68).
“The law is not administered without the gospel, nor 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).