The weekly Sabbath day, the holy time of rest that falls every seven days—from Friday sunset to Saturday sunset—was made and set apart for man at the time of man's creation. God blessed and sanctified the seventh day, and in it He rested from all His works of the creation week prior, as recorded in Genesis 1.
The sunset-to-sunset reckoning comes from the fact that the preceding six days each began in the evening (Genesis 1:5 Genesis 1:5And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.
American King James Version×; Genesis 1:8 Genesis 1:8And God called the firmament Heaven. And the evening and the morning were the second day.
American King James Version×; Genesis 1:13 Genesis 1:13And the evening and the morning were the third day.
American King James Version×; Genesis 1:19 Genesis 1:19And the evening and the morning were the fourth day.
American King James Version×; Genesis 1:23 Genesis 1:23And the evening and the morning were the fifth day.
American King James Version×; Genesis 1:31 Genesis 1:31And God saw every thing that he had made, and, behold, it was very good. And the evening and the morning were the sixth day.
American King James Version×), and in Leviticus 23:32 Leviticus 23:32It shall be to you a sabbath of rest, and you shall afflict your souls: in the ninth day of the month at even, from even to even, shall you celebrate your sabbath.
American King James Version×God explains that He still reckons days this way. (The custom of beginning and ending days at midnight dates back to practices established in pagan Roman society and is contrary to God's method of determining time.)
The first Sabbath was the day after the formation of the first man and woman, an ordained time for human beings to focus on a close personal relationship with their Maker (Genesis 1:26-2 Genesis 1:26-2
American King James Version×:3).
Jesus Christ declared Himself the Lord of the Sabbath (Mark 2:28 Mark 2:28Therefore the Son of man is Lord also of the sabbath.
American King James Version×), and indeed He is the One who actually instituted the Sabbath, God the Father having created all things through Him (John 1:1-3 John 1:1-3  In the beginning was the Word, and the Word was with God, and the Word was God.  The same was in the beginning with God.  All things were made by him; and without him was not any thing made that was made.
American King James Version×; John 1:14 John 1:14And the Word was made flesh, and dwelled among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.
American King James Version×; Colossians 1:16-17 Colossians 1:16-17  For by him were all things created, that are in heaven, and that are in earth, visible and invisible, whether they be thrones, or dominions, or principalities, or powers: all things were created by him, and for him:  And he is before all things, and by him all things consist.
American King James Version×; Hebrews 1:1-2 Hebrews 1:1-2  God, who at sundry times and in divers manners spoke in time past to the fathers by the prophets,  Has in these last days spoken to us by his Son, whom he has appointed heir of all things, by whom also he made the worlds;
American King James Version×).
As Jesus also explained in the same instance, the Sabbath was intended to directly benefit all mankind—not just one particular cultural, religious or ethnic group (Mark 2:27 Mark 2:27And he said to them, The sabbath was made for man, and not man for the sabbath:
American King James Version×). It is a very special time to deepen and broaden man's devotion to and relationship with God. When we turn from seeking our own way, we find pleasure in that which pleases God (Isaiah 58:13-14 Isaiah 58:13-14  If you turn away your foot from the sabbath, from doing your pleasure on my holy day; and call the sabbath a delight, the holy of the LORD, honorable; and shall honor him, not doing your own ways, nor finding your own pleasure, nor speaking your own words:  Then shall you delight yourself in the LORD; and I will cause you to ride on the high places of the earth, and feed you with the heritage of Jacob your father: for the mouth of the LORD has spoken it.
American King James Version×).
God gave instructions concerning the observance of the Sabbath when He listed it with the Ten Commandments in Exodus 20 and Deuteronomy 5. Thus it is an important aspect of God's law, which we are to obey.
In Exodus 20:8-10 Exodus 20:8-10  Remember the sabbath day, to keep it holy.
 Six days shall you labor, and do all your work:
 But the seventh day is the sabbath of the LORD your God: in it you shall not do any work, you, nor your son, nor your daughter, your manservant, nor your maidservant, nor your cattle, nor your stranger that is within your gates:
American King James Version×, God said that man is to "remember the Sabbath day, to keep it holy." We remember and hallow the Sabbath by refraining from work during that time and instead using it to seek after God and worship Him.
Leviticus 23:3 Leviticus 23:3Six days shall work be done: but the seventh day is the sabbath of rest, an holy convocation; you shall do no work therein: it is the sabbath of the LORD in all your dwellings.
American King James Version×lists the seventh-day Sabbath as one of God's appointed times and declares it a period of solemn rest and of holy convocation—a mandated sacred assembly. As Christians follow this pattern of observance and worship, they are reminded of the Creator God, the One who brought them into being.
In Deuteronomy 5:12-15 Deuteronomy 5:12-15  Keep the sabbath day to sanctify it, as the LORD your God has commanded you.
 Six days you shall labor, and do all your work:
 But the seventh day is the sabbath of the LORD your God: in it you shall not do any work, you, nor your son, nor your daughter, nor your manservant, nor your maidservant, nor your ox, nor your ass, nor any of your cattle, nor your stranger that is within your gates; that your manservant and your maidservant may rest as well as you.
 And remember that you were a servant in the land of Egypt, and that the LORD your God brought you out there through a mighty hand and by a stretched out arm: therefore the LORD your God commanded you to keep the sabbath day.
American King James Version×God reemphasizes the need to keep the Sabbath. He explains that the Sabbath is to be a reminder not only of Him as the Creator, but of the fact that He is the One who frees from bondage (see also Luke 4:18-19 Luke 4:18-19  The Spirit of the Lord is on me, because he has anointed me to preach the gospel to the poor; he has sent me to heal the brokenhearted, to preach deliverance to the captives, and recovering of sight to the blind, to set at liberty them that are bruised,  To preach the acceptable year of the Lord.
American King James Version×). Ancient Israel remembered being freed from physical bondage in Egypt. Christians remember being freed from spiritual bondage and liberated through Jesus Christ (Romans 6:16-18 Romans 6:16-18  Know you not, that to whom you yield yourselves servants to obey, his servants you are to whom you obey; whether of sin to death, or of obedience to righteousness?  But God be thanked, that you were the servants of sin, but you have obeyed from the heart that form of doctrine which was delivered you.  Being then made free from sin, you became the servants of righteousness.
American King James Version×).
Exodus 31:13-17 Exodus 31:13-17  Speak you also to the children of Israel, saying, Truly 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 does sanctify you.
 You shall keep the sabbath therefore; for it is holy to you: every one that defiles it shall surely be put to death: for whoever does any work therein, that soul shall be cut off from among his people.
 Six days may work be done; but in the seventh is the sabbath of rest, holy to the LORD: whoever does any work in the sabbath day, he shall surely be put to death.
 Why the children of Israel shall keep the sabbath, to observe the sabbath throughout their generations, for a perpetual covenant.
 It is a sign between me and the children of Israel for ever: for in six days the LORD made heaven and earth, and on the seventh day he rested, and was refreshed.
American King James Version×points out that the Sabbath is a sign between God and His people and constitutes a perpetual covenant. This is in addition to the instruction given at the time of man's creation and in the Ten Commandments. The Sabbath is to be kept holy as a reminder to those called of God that He is the one true God who sets them apart and that they are His children who have surrendered their lives in obedience to Him.
When Jesus returns to the earth and establishes the rule of the Kingdom of God over all nations, the Sabbath will be regularly observed by all humankind as a means of worshipping and serving Him (Isaiah 66:23 Isaiah 66:23And it shall come to pass, that from one new moon to another, and from one sabbath to another, shall all flesh come to worship before me, said the LORD.
American King James Version×).
Jesus Himself set a righteous example in His life of observing the Sabbath (Luke 4:31 Luke 4:31And came down to Capernaum, a city of Galilee, and taught them on the sabbath days.
American King James Version×), and the New Testament records that His followers continued that practice long after His death and resurrection.
Paul taught the gentiles (non-Israelites) on the Sabbath (Acts 13:42-44 Acts 13:42-44  And when the Jews were gone out of the synagogue, the Gentiles sought that these words might be preached to them the next sabbath.
 Now when the congregation was broken up, many of the Jews and religious proselytes followed Paul and Barnabas: who, speaking to them, persuaded them to continue in the grace of God.
 And the next sabbath day came almost the whole city together to hear the word of God.
American King James Version×), following both the law of God and the example of Christ. Wherever Paul went he taught on the Sabbath, as was his custom, and established churches that kept the Sabbath (Acts 17:2 Acts 17:2And Paul, as his manner was, went in to them, and three sabbath days reasoned with them out of the scriptures,
American King James Version×; Acts 18:4). No example can be found in the writings of the apostles or the practice of the New Testament Church that shows any hint of change in the example and teaching they received from Christ.
Hebrews 4:9 Hebrews 4:9There remains therefore a rest to the people of God.
American King James Version×declares that "there remains a Sabbath rest for the people of God" (NASB). The context of this passage, Hebrews 3-4, presents the seventh-day Sabbath as symbolic of the rest that the ancient Israelites sought—fulfilled in part in their settlement in the Promised Land, but to be ultimately fulfilled in the future rule of God over all nations, when all peoples will find true rest. Nearby verses show that Christians now are to be diligent to enter God's future rest as well as the weekly rest that prefigures it (Hebrews 4:4 Hebrews 4:4For he spoke in a certain place of the seventh day on this wise, And God did rest the seventh day from all his works.
American King James Version×; Hebrews 4:9-11 Hebrews 4:9-11  There remains therefore a rest to the people of God.  For he that is entered into his rest, he also has ceased from his own works, as God did from his.  Let us labor therefore to enter into that rest, lest any man fall after the same example of unbelief.
American King James Version×).
In conclusion, the Sabbath looks back to creation and reminds man of his Creator. In the present, it recalls for those who keep the seventh day holy that God is the One who has delivered them from the bondage of sin. Finally, the Sabbath looks forward to the return of Jesus Christ and the establishment of the Kingdom of God, when there will be true rest for all humanity.