The Sabbath is the seventh day of the week, which is Saturday in our modern calendar. The Hebrew word is related to the words for seven and seventh. Its origin is found in the week in which God created the heaven and the earth (Gen 1:1-2:3). God created for six days and rested on the seventh. He did not rest because He was tired. It means He ceased His work of creating. The Lord set up this pattern and others in the creation. The first time the word Sabbath appears in the Bible is in Exodus 16:23-29 in relation to the collection of manna in the wilderness. Apparently the concept was already understood. Soon after, it became part of the law of Moses called the Sabbath in the ten commandments (Ex 20:8-11). This passage states that that Sabbath was based on the creation week. When Moses later reiterated t he ten commandment to the next generation as they were nearing the time of entering the promised land, he said the Sabbath was to remind the Israelites that God brought them out of Egypt. This indicates that the Sabbath served to teach them that they were a special people with a different set of values and lifestyle than the other nations. It was a very serious institution. For example, when a man dishonored the Sabbath by collecting sticks, he was executed as an example (Num 15:32-37). When Gentiles were trying to conduct business on the Sabbath with the Jews at the wall Nehemiah had built, he drove them off under threat of attack (Neh 13:15-21).
Some people think the Sabbath applies to Christians in the New Testament. They base this on the fact that the Sabbath was based on the creation week, and that it was part of the ten commandments. However, the civil and ceremonial parts of the law of Moses did not carry over into the New Testament. That is why we do not carry out the punishments prescribed in the law for various offenses, and why we no longer do things such as offer animal sacrifices. The ceremonial parts of the law were fulfilled in Jesus Christ. Jesus did not come to destroy the law, but to fulfill it (Mt 5:17). In fact, the rest of Matthew 5 is Jesus explaining how He calls us to the spiritual fulfillment of the intent of the law, not just to the obedience of the outward actions.
There was a debate that arose in the early church about whether or not Gentile Christians needed to be circumcised in order to be part of the people of God. God gave Abraham the covenant of circumcision and it applied to his descendants as well (Gen 17). There was a conference of the leaders of the early church to resolve this issue (Acts 15). It was decided that only four prohibitions would be placed on the Gentile Christians - abstaining from idolatry and fornication, and from eating strangled things and blood (Acts 15:19-21). This is obviously not an exhaustive list, but there was nothing about the Sabbath. This issue did not go away at that time (Rom 2:25-29, Rom 4:9-12, 1Cor 7:19, Gal 2:7-12, Gal 5:6 &11, Phil 3:2-3, Titus 1:10). Man is always trying to turn relationship with God into religion, and God is always trying lead men out of religion into relationship. Paul later wrote quite a bit in his epistles about the Gentiles' relationship with the Old Testament and never said anything about having to keep the Sabbath. He said it was not necessary (Rom 14:5-6, Gal 4:10, Col 2:16-17). He also warned repeatedly about reverting back to outward religiosity and missing the spiritual meaning of having a relationship with God (Gal 2-4, Col 2:8-23). He taught that the law was a symbolic way of pointing us to Jesus Christ and the fulfillment of its meaning (Gal 3:24, Heb 8-10 - actually the whole book of Hebrews). He specifically taught the symbolic nature of the Sabbath (Heb 3:11-4:11). The hypocritical Jews had perverted the meaning of the Sabbath to where men became the servants of their interpretation of the outward application of it, and lost its true purpose (Mk 2:27). Jesus healed people several times on the Sabbath (Mk 1:21-31, Mk 12:10-12, Lk 13:10-16, Lk 14:1-5, Jn 5:1-18, Jn 9:14-16). They saw this as a violation of the law, and were so enraged they labeled Him a false teacher and plotted to kill Him over it.
The Sabbath was to represent the spiritual rest the Lord provides through His Spirit. Isaiah 28:11-12 talks about stammering lips and another tongue which would give rest. Paul quoted this in 1Corinithians 14:21 to mean speaking in tongues by the Holy Ghost. Jesus promised that we would find rest in Him for our souls, not just our bodies (Mt 11:28-30). He called the gift of His Spirit the Comforter (Jn 14:16 & 26, Jn 15:26, Jn 16:7). The Sabbath also symbolizes the future rest the people of God will enter into after the second coming of Christ (2Thes 1:7, Heb 3:11-4:11, Rev 14:13).