“a holy Sabbath.” This is the first time in the Bible that the word “Sabbath” is used, and so God has to describe it as a “day of rest.” Although the REV capitalizes “Sabbath,” it is possible that the better choice would be to simply have “sabbath” in this verse because the formal weekly “Sabbath” was just being put in place. This is the first time a regular weekly rest was mentioned, then in the Ten Commandments, “the Sabbath” became clarified and set forth as part of the Old Covenant and Mosaic Law.
[For more on the Sabbath, see commentary on Exodus 20:10.]