In his helpful book, An Exposition of the Westminster Confession of Faith, Robert Shaw (d. 1863) discussed the Mosiac (or Sinaitic) covenant in a way similar to Francis Turretin and other Reformed theologians. Here’s what Shaw wrote in his comments on WCF 19.2.
“It may be remarked, that the law of the ten commandments was promulgated to Israel from Sinai in the form of a covenant of works. Not that it was the design of God to renew a covenant of works with Israel, or to put them upon seeking life by their own obedience to the law; but the law was published to them as a covenant of works, to show them that without a perfect righteousness, answering to all the demands of the law, they could not be justified before God; and that, finding themselves wholly destitute of that righteousness, they might be excited to take hold of the covenant of grace, in which a perfect righteousness for their justification is graciously provided.”
“The Sinai transaction was a mixed dispensation. In it the covenant of grace was published, as appears from these words in the preface standing before the commandments; ‘I am the Lord thy God, which have brought thee out of the land of Egypt, out of the house of bondage;’ and from the promulgation of the ceremonial law at the same time. But the moral law, as a covenant of works, was also displayed, to convince the Israelites of their sinfulness and misery, to teach them the necessity of an atonement, and lead them to embrace by faith the blessed Mediator, the Seed promised to Abraham, in whom all the families of the earth were to be blessed.”
“The law, therefore, was published at Sinai as a covenant of works in subservience to the covenant of grace. And the law is still published in subservience to the gospel, as ‘a schoolmaster to bring sinners to Christ, that they may be justified by faith’ (Gal. 3:24).”
Robert Shaw, An Exposition of the Westminster Confession of Faith (Ross-shire: Christian Focus, 2008), 256. For more info on this topic, be sure to see Michael Brown’s Christ and the Condition.