Moreover also I gave them my sabbaths, to be a sign between me and them, that they might know that I am the LORD that sanctify them.

Wesley's Notes

20:12 A sign - Of their being peculiarly my people.

Jamieson-Fausset-Brown Bible Commentary

12. sabbaths, . a sign between me and them-a kind of sacramental pledge of the covenant of adoption between God and His people. The Sabbath is specified as a sample of the whole law, to show that the law is not merely precepts, but privileges, of which the Sabbath is one of the highest. Not that the Sabbath was first instituted at Sinai, as if it were an exclusively Jewish ordinance (Ge 2:2, 3), but it was then more formally enacted, when, owing to the apostasy of the world from the original revelation, one people was called out (De 5:15) to be the covenant-people of God.

sanctify them-The observance of the Sabbath contemplated by God was not a mere outward rest, but a spiritual dedication of the day to the glory of God and the good of man. Otherwise it would not be, as it is made, the pledge of universal sanctification (Ex 31:13-17; Isa 58:13, 14). Virtually it is said, all sanctity will flourish or decay, according as this ordinance is observed in its full spirituality or not.

Matthew Henry's Concise Commentary

20:10-26. The history of Israel in the wilderness is referred to in the new Testament as well as in the Old, for warning. God did great things for them. He gave them the law, and revived the ancient keeping of the sabbath day. Sabbaths are privileges; they are signs of our being his people. If we do the duty of the day, we shall find, to our comfort, it is the Lord that makes us holy, that is, truly happy, here; and prepares us to be happy, that is, perfectly holy, hereafter. The Israelites rebelled, and were left to the judgments they brought upon themselves. God sometimes makes sin to be its own punishment, yet he is not the Author of sin: there needs no more to make men miserable, than to give them up to their own evil desires and passions.