From Louis Berkhof's Systematic Theology pg. 292
pg. 298-299 cont.
In the Patriarchal period the gracious character of the Covenant [of Grace] stood out more prominently than in the later period. The promise was more in the foreground, Rom. 4:13, Gal 3:18. Yet even this should not be stressed unduly as if there were no legal burdens, both moral and ceremonial, before the time of Moses, and no gracious promises during the period of the law. The substance of the law was in force before Moses and sacrifices were already required and gracious promises are found in great abundance in the post-Mosiac writings. The only real point of difference is this: because the law constituted for Israel an explicit reminder of the demands of the covenant of works, there was a greater danger of mistaking the way of the law for the way of salvation. And the history of Israel teaches us that they did not escape the danger.
The Siniatic covenant included a service that contained a positive reminder of the strict demands of the covenant of works. The law was placed very much in the foreground, giving prominence once more to the earlier legal element. But the covenant of Sinai was not a renewal of the covenant of works; in it the law was made subservient to the covenant of grace. This is indicated already in the introduction to the ten commandments, Ex. 20:2, Deut 5:6, and further in Rom. 3:20, Gal 3:24. It is true that at Sinai a conditional element was added to the covenant, but it was not the salvation of the Israelite but his theocratic standing in the nation, and the enjoyment of external blessings that was made dependent on the keeping of the law, Deut 28:1-14. The law served a twofold purpose in connection with the covenant of grace. (1) to increase the consciousness of sin, Rom. 3:20, 4:15, Gal 3:19, and (2) to be a tutor unto Christ, Gal 3:24.
pg. 298-299 cont.
There have been several deviating opinions respecting the Siniatic covenant which deserve attention...
c. Still others are of the opinion that God established three covenants at Sinai, a national covenant, a covenant of works, and a covenant of grace. The first made with all the Israelites and was the continuation of the particularistic line which began with Abraham. In it God demands external obedience and promises temporal blessings. The second was a repetition of the covenant of works by the giving of the Decalogue. And the last a renewal of the covenant of grace as it was established with Abraham in the giving of the ceremonial law.