Remember the sabbath day, to keep it holy. Six days you shall labor, and do all your work; but the seventh day is a sabbath to the Lord your God; in it you shall not do any work, you, or your son, or your daughter, your manservant, or your maidservant, or your cattle, or the sojourner who is within your gates; for in six days the Lord made heaven and earth, the sea, and all that is in them, and rested the seventh day; therefore the Lord blessed the sabbath day and hallowed it. (Exodus 20:8-11)
Observe the sabbath day, to keep it holy, as the Lord your God commanded you. Six days you shall labor, and do all your work; but the seventh day is a sabbath to the Lord your God; in it you shall not do any work, you, or your son, or your daughter, or your manservant, or your maidservant, or your ox, or your [donkey], or any of your cattle, or the sojourner who is within your gates, that your manservant and your maidservant may rest as well as you. You shall remember that you were a servant in the land of Egypt, and the Lord your God brought you out thence with a mighty hand and an outstretched arm; therefore the Lord your God commanded you to keep the sabbath day. (Deuteronomy 5:12-15)
From the first passage (Exodus), it can be seen that a weekly holy day was designed after the work-rest pattern of God, who created the universe over the course of six days and then rested on the seventh day. (Genesis 2:1-3)
From the second passage (Deuteronomy), it can be seen that, as part of the Old Covenant, God commanded that the Jews observe Saturday as their weekly holy day because the Jews were miraculously liberated by God from their Egyptian slavery on a Saturday.
That part of the Old Covenant, the observance of a weekly holy day on Saturday, like circumcision and kosher food laws, was abrogated when the New Covenant was established by Jesus Christ. Instead, Sunday was established by the New Covenant Church as their weekly holy day because mankind was miraculously liberated from their slavery to sin and death when Jesus definitively rose from the dead on a Sunday.
That the Old Covenant requirement concerning the observance of a weekly holy day on Saturday was abrogated when the New Covenant was established can be seen in the absence of any explicit command by Jesus or his Apostles to observe the Sabbath and by the words of St Paul against judging others on the basis of whether or not they observe Jewish holy days and his condemnation of those who thought the observance of Jewish holy days was absolutely necessary to salvation:
Therefore let no one pass judgment on you in questions of food and drink or with regard to a festival or a new moon or a sabbath. These are only a shadow of what is to come; but the substance belongs to Christ. (Colossians 2:16-17)
Who are you to pass judgment on the servant of another? It is before his own master that he stands or falls. And he will be upheld, for the Master is able to make him stand. One man esteems one day as better than another, while another man esteems all days alike. Let every one be fully convinced in his own mind. He who observes the day, observes it in honor of the Lord. … Why do you pass judgment on your brother? (Romans 14:4-6,10)
You observe days, and months, and seasons, and years! I am afraid I have labored over you in vain. (Galatians 4:10-11)