“Speak also unto the children of Israel, saying, Verily my Sabbaths you shall keep: for it is a sign between me and you throughout your generations; that you may know that I am the LORD that sanctifies you” Exodus 31:13
God set apart one day from the rest; six days man was to work and on the seventh rest. Man was to labor with his hands for the food he needed to live but on the seventh day he was to trust completely in God. That is not to say he did not have to trust God during the other six days, but one day was set apart to rest from labor and concentrate only on God.
A person who labors should labor for God, one who rests should rest for God; God was establishing a principle that man was to live by – the principle of separation. Man was created for God but in a fallen world men live for themselves and a host of idols that take their hearts away from God.
The saved individual is sanctified by God or set apart from the world that is corrupt in its affections.