After the deaths of Jacob and Joseph, the children of Israel became slaves in Egypt. "So the Egyptians made the children of Israel serve with rigor: And they made their lives bitter with hard bondage—in mortar, in brick, and in all manner of service in the field" (Exodus 1:13-14).
The Egyptians, observing no Sabbath, lashed the Israelites in their slave labor on the Sabbaths just as on other days. The Israelites, then, for several generations, were not permitted to keep the Sabbath. They probably received no organized religious teaching in all that time. They likely had no written record of God's instruction to the patriarchs before them.
The generation of Israelites that Moses led out of Egypt knew little, if anything, about the Sabbath. Time could have been lost—to them. However, God reestablished the right knowledge of the Sabbath through a series of miracles.
The Israelites came to the wilderness of Sin two months after leaving Egypt, and two weeks before arriving at Mount Sinai, when God gave them the Ten Commandments and made a covenant with them. Notice, His instruction concerning the Sabbath predates the giving of the law and the Old Covenant!
Here God reveals to them, miraculously, which day is the Sabbath and whether it makes any difference if we keep it:
Although this happens before they receive the Ten Commandments (Exodus 20) or the Old Covenant is proposed, God's law is in full force and effect. God is testing them to see if they will obey one of its critical points.
Notice what happens. Some try to save a supply of manna over until the next morning, contrary to God's command. "It bred worms and stank" (verse 20). On the sixth day, they gather a double portion of manna, and Moses explains why: "Tomorrow is a Sabbath rest, a holy Sabbath to the Lord" (verse 23). On the sixth day, then, they gather a supply of food for the Sabbath as well.
Miraculously, it does not breed worms or decay, as on all the other days (verse 24)! By this sign, God identifies which day is the Sabbath. Thus, Moses says: "Today is a Sabbath to the Lord; today you will not find it in the field. Six days you shall gather it, but on the seventh day, which is the Sabbath, there will be none" (verses 25-26).
Did it make any difference? It sure did!
Was it all right for some to go ahead and work on the seventh day, and then rest on the first day of the week? Just like most professing Christians today, some of these Israelites thought they knew better! Notice: "Some of the people went out on the seventh day to gather, but they found none." They thought the day they observed, or if they kept it at all, made no difference.
But it made a difference to God! On the six weekdays, God Himself had accomplished the work of raining down manna, but not on His Sabbath, which is holy to Him. On the seventh day, God rested from sending them manna! Notice verses 28-29:
It certainly does make a difference to God! He is the same today as He was yesterday and will be forever (Hebrews 13:8)! It still makes a difference!
God reveals through these miracles which day is His day—His Sabbath. Manna fell for six days—but none on the seventh day. For nearly forty years, God reminded them every week which day He had set apart. If they forgot, they did not eat!
This example also shows that keeping the Sabbath holy is part of His eternal law, for it occurs many days before He proposes the Old Covenant at Sinai. In this way, God reveals both which day His Sabbath is and that the keeping or breaking of it does make a difference. Failing to keep God's holy Sabbath is sin, and its penalty is death (Romans 6:23)!
Finally, notice Exodus 16:29: "For the Lord has given you the Sabbath." Nowhere in all God's Word is it said, "The Lord has given you Sunday," or "The Lord has given you the first day of the week." Who, then, gave the professing Christian world its Sunday worship? The answer appears in "church" history—carnal, pagan man, under the leadership of Constantine and in rebellion against God, gave professing "Christianity" Sunday worship several centuries after Christ died. Sunday-worship came out of paganism, and the world still follows the custom!
Maybe you should ask yourself, "What is the source of my religion?" Is it human reason, public opinion, or the traditions of man? Or is the Creator God the source of what you believe and practice?