The subject of this chapter is the Sabbath. Here, God begins the process of revealing to them which day is the Sabbath by bringing a double portion of manna on the day before, and on the Sabbath day, no manna at all. Of course, some of the people try to gather manna on the Sabbath day. Thus, God responds, in verse 28, the way He does. Besides His obvious exasperation, in asking, "How long?" He is implying that the Sabbath already existed by this time—indeed, since creation!
Israel, as a nation, began breaking the Sabbath from the get-go. Even before they reached Sinai, they were already rejecting the fourth commandment.
John W. Ritenbaugh
Sabbathkeeping (Part 2)
Because God rested after six days of labor, the Sabbath is also our day of rest and a memorial of Creation. He wants us to remember, not only what He did in the physical creation, but also that His spiritual creation continues in us now. When God blessed and sanctified the seventh day, He made it holy, set apart for God's use! Only God can make a day holy, and He does this by putting Himself, through His Spirit, into it.
We are then instructed to "keep" it holy. Various scriptures give examples of things God prohibits on His Sabbath: working, cooking, carrying burdens. God does not make a comprehensive list of "dos and don'ts" for us to follow. Instead, He gives us principles of what is proper and improper Sabbath behavior, and we then must use God's Spirit to decide our actions.
Martin G. Collins
The Fourth Commandment
Other Forerunner Commentary entries containing Exodus 16:28: