We find the first mention of the Sabbath in the second chapter of Genesis, the book of beginnings. After recounting how God created everything in six days in the first chapter, we read: "Thus the heavens and the earth were finished, and all the host of them. And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made. And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made." -Genesis 2:1-3, KJV, emphasis mine
In reading these verses, we immediately notice that the Sabbath is inextricably linked to the cessation of God's work and the act of resting. Likewise, we find that this notion is further reinforced when God introduces the Sabbath to the Israelites in the sixteenth chapter of Exodus. After giving them manna to eat, we read there: "And he [Moses] said unto them, This is that which the Lord hath said, To morrow is the rest of the holy sabbath unto the Lord: bake that which ye will bake to day, and seethe that ye will seethe; and that which remaineth over lay up for you to be kept until the morning. And they laid it up till the morning, as Moses bade: and it did not stink, neither was there any worm therein. And Moses said, Eat that to day; for to day is a sabbath unto the Lord: to day ye shall not find it in the field. Six days ye shall gather it; but on the seventh day, which is the sabbath, in it there shall be none. And it came to pass, that there went out some of the people on the seventh day for to gather, and they found none. And the Lord said unto Moses, How long refuse ye to keep my commandments and my laws? See, for that the Lord hath given you the sabbath, therefore he giveth you on the sixth day the bread of two days; abide ye every man in his place, let no man go out of his place on the seventh day. So the people rested on the seventh day." -Exodus 16:23-30, KJV, emphasis mine
Then, when God gave Moses the Ten Commandments on Mount Sinai, we find again that element of ending work and resting. We read there: "Remember the sabbath day, to keep it holy. Six days shalt thou labour, and do all thy work: But the seventh day is the sabbath of the Lord thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates: For in six days the Lord made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the Lord blessed the sabbath day, and hallowed it." - Exodus 20:8-11, KJV, emphasis mine
Indeed, this notion of resting from one's work on the Sabbath is apparent throughout the writings of the Old Testament. But did this notion carry over to the New Testament? Is there any application of this principle for Christians?
We know that the earliest Christian churches were entirely Jewish, and that they continued to observe the Jewish Sabbath. However, as Christianity began to spread to Gentile populations who didn't have any personal knowledge of the Sabbath or any tradition of observing it, the relevance of the Sabbath declined rapidly as Jewish Christians became a minority within the church. And this is the situation that was taken up by the anonymous author of the epistle to the Hebrews.
After admonishing his audience to "consider the Apostle and High Priest of our profession, Christ Jesus" (Hebrews 3:1, KJV), the author instructs them to take a look at the experience of the Hebrews as they approached the Promised land (same chapter). He admonishes them not to follow their example of disbelief and stubbornness and reminds them that God did not permit that generation to enter into his rest (same chapter). In other words, the author is invoking the old notion of resting from work.
In the following chapter, the author summarizes the concept for his Christian audience and hearkens back to something that Jesus Christ had said during his earthly ministry. We read there: "Let us therefore fear, lest, a promise being left us of entering into his rest, any of you should seem to come short of it. For unto us was the gospel preached, as well as unto them: but the word preached did not profit them, not being mixed with faith in them that heard it. For we which have believed do enter into rest, as he said, As I have sworn in my wrath, if they shall enter into my rest: although the works were finished from the foundation of the world. For he spake in a certain place of the seventh day on this wise, And God did rest the seventh day from all his works. And in this place again, If they shall enter into my rest. Seeing therefore it remaineth that some must enter therein, and they to whom it was first preached entered not in because of unbelief: Again, he limiteth a certain day, saying in David, To day, after so long a time; as it is said, To day if ye will hear his voice, harden not your hearts. For if Jesus had given them rest, then would he not afterward have spoken of another day. There remaineth therefore a rest to the people of God. For he that is entered into his rest, he also hath ceased from his own works, as God did from his. Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief." - Hebrews 4:1-11, KJV, emphasis mine
In the gospel according to Matthew, we read that Christ issued an invitation to the weary sea of humanity that stood before him. He said: "Come unto me, all ye that labour and are heavy laden, and I will give you rest. Take my yoke upon you, and learn of me; for I am meek and lowly in heart: and ye shall find rest unto your souls. For my yoke is easy, and my burden is light." -Matthew 11:28-30, KJV, emphasis mine
This then is the notion of the Sabbath that is still relevant to all Christians: We must stop doing our own works and rest in Christ - We must lay down our own burdens and replace them with his featherlight mantle - We must cease to rely on our own understanding and learn of him!