READ: Ex. 16:22–36: … See! For the Lord has given you the Sabbath; therefore He gives you on the sixth day bread for two days. Let every man remain in his place … So the people rested on the seventh day …
Israel also receives instructions on how to deal with food gathering concerning the Sabbath. Verses 5 and 22 show that Israel was already familiar with the institution of the holy Sabbath — even before the Ten Commandments were given at Mount Horeb!
The double gathering of manna on Friday, in relation to the Sabbath, serves as a test of whether they will obey God’s law (v.4). What law is this? It’s the law that they must gather a double portion the day before the Sabbath.
So, the Sabbath was not first instituted at Mount Horeb as part of the Ten Commandments. No — its institution dates back to Genesis 2:2–3. The LORD thus refers in the wilderness to something already established.
Moses calmly tells the people that the next day is the day of rest — the holy Sabbath to the LORD. Most likely, the Sabbath had fallen into disuse in Egypt. But now the people must again walk with the LORD as He desires. That requires constant instruction and correction.
This becomes evident when some — in direct disobedience — go out to gather food on the Sabbath: they find nothing.
The LORD also wants to teach future generations. They must always remember Who He is and how He cares for them. To ensure lasting remembrance of His special care, the LORD commands that a gomer of manna be kept before Him; later this would be stored in the Ark of the Covenant (v.33; Hebrews 9:4).
The manna, as bread from heaven, would later serve as a foreshadowing of Christ, the true Bread from heaven (John 6), through whom true life is given.