Thanks to Logos Reformed, I’ve been enjoying the first two volumes of Geerhardus Vos’ Reformed Dogmatics (English translation). In these volumes, and among other things, Vos discusses Reformed covenant theology extensively (the covenant of redemption, the covenant of works, and the covenant of grace). Here’s a section of Vos’ longer discussion on the place of the Mosaic covenant – the covenant God made with Israel on Sinai.
“The Sinaitic covenant is not a new covenant as concerns the essence of the matter, but the old covenant of grace established with Abraham in somewhat changed form….”
“The covenant with Israel served in an emphatic manner to recall the strict demands of the covenant of works. To that end, the law of the Ten Commandments was presented so emphatically and engraved deeply in stone. This law was not, as Cocceius meant, simply a form for the covenant of grace. It truly contained the content of the covenant of works. But—and one should certainly note this—it contains this content as made serviceable for a particular period of the covenant of grace. It therefore says, for example, “I am the Lord your God.” Therefore, it also contains expressions that had reference specifically to Israel, and thus are not totally applicable to us (e.g., “that it may be well with you in the land that the Lord your God gives you”).”
“But also, beyond the Decalogue, there is reference to the law as a demand of the covenant of works (e.g., Lev 18:5; Deut 27:26; 2 Cor 3:7, 9). It is for this reason that in the last cited passage, Paul calls the ministry of Moses a ministry of condemnation. This simply shows how the demand of the law comes more to the fore in this dispensation of the covenant of grace. This ministry of the law had a twofold purpose: 1) It is a disciplinarian until Christ. 2) It serves to multiply sin, that is, both to lure sin out from its hidden inner recesses as well as to bring it to consciousness (cf. Gal 3:19; Rom 4:15; 5:13). Paul teaches expressly that the law did not appear here as an independent covenant of works in Gal 3:19ff. That the law is also not a summary of the covenant of grace appears from the absence of the demand of faith and of the doctrine of the atonement.”
Finally, Vos’ Reformed Dogmatics are not for sale individually quite yet at Logos Reformed, but the volumes 1-2 are included in some Logos Reformed package deals. The above quote is found in Vos, Geerhardus. Reformed Dogmatics. Ed. Richard B. Gaffin & Richard de Witt. Trans. Annemie Godbehere et al. Vol. 2. Bellingham, WA: Lexham Press, 2013, pp 76-77.