Verses are quoted from the English Standard Version
The three annual religious feasts in the law of Moses had worship services on both Sunday and Saturday:
o Exo 12:16 On the first day [of Passover] you shall hold a holy assembly, and on the seventh day a holy assembly. No work shall be done on those days. But what everyone needs to eat, that alone may be prepared by you.
o Lev 23:35-43 On the first day [of Pentecost] shall be a holy convocation; you shall not do any ordinary work. 36 For seven days you shall present food offerings to the LORD. On the eighth day you shall hold a holy convocation and present a food offering to the LORD. It is a solemn assembly; you shall not do any ordinary work. 37 "These are the appointed feasts of the LORD, which you shall proclaim as times of holy convocation, for presenting to the LORD food offerings, burnt offerings and grain offerings, sacrifices and drink offerings, each on its proper day, 38 besides the LORD's Sabbaths and besides your gifts and besides all your vow offerings and besides all your freewill offerings, which you give to the LORD. 39 "On the fifteenth day of the seventh month, when you have gathered in the produce of the land, you shall celebrate the feast of the LORD seven days [Feast of Booths]. On the first day shall be a solemn rest, and on the eighth day shall be a solemn rest. 40 And you shall take on the first day the fruit of splendid trees, branches of palm trees and boughs of leafy trees and willows of the brook, and you shall rejoice before the LORD your God seven days. 41 You shall celebrate it as a feast to the LORD for seven days in the year. It is a statute forever throughout your generations; you shall celebrate it in the seventh month. 42 You shall dwell in booths for seven days. All native Israelites shall dwell in booths, 43 that your generations may know that I made the people of Israel dwell in booths when I brought them out of the land of Egypt: I am the LORD your God."
o Num 28:18 On the first day [of Passover] there shall be a holy convocation. You shall not do any ordinary work,
o Num 29:1 "On the first day of the seventh month you shall have a holy convocation. You shall not do any ordinary work. It is a day for you to blow the trumpets,
o Neh 8:18 And day by day, from the first day to the last day, he read from the Book of the Law of God. They kept the feast seven days, and on the eighth day there was a solemn assembly, according to the rule.
o Matt. 26:17 Now on the first day of Unleavened Bread the disciples came to Jesus, saying, "Where will you have us prepare for you to eat the Passover?"
o Mark 14:12 And on the first day of Unleavened Bread, when they sacrificed the Passover lamb, his disciples said to him, "Where will you have us go and prepare for you to eat the Passover?"
Additional Old Testament Week-long Consecration ceremonies included worship assemblies on both Sunday and Saturday:
o Lev 9:1-5 On the eighth day Moses called Aaron and his sons and the elders of Israel, 2 and he said to Aaron, "Take for yourself a bull calf for a sin offering and a ram for a burnt offering, both without blemish, and offer them before the LORD. 3 And say to the people of Israel, 'Take a male goat for a sin offering, and a calf and a lamb, both a year old without blemish, for a burnt offering, 4 and an ox and a ram for peace offerings, to sacrifice before the LORD, and a grain offering mixed with oil, for today the LORD will appear to you.'" 5 And they brought what Moses commanded in front of the tent of meeting, and all the congregation drew near and stood before the LORD.
o 2 Chron. 29:17 They began to consecrate on the first day of the first month, and on the eighth day of the month they came to the vestibule of the LORD. Then for eight days they consecrated the house of the LORD, and on the sixteenth day of the first month they finished.
o Firstborn animals and sons were to be concsecrated to the Lord on the 8th Day as well in a special ceremony.
The Command in the 10 Commandments emphasizes one day in seven rather than a particular day
o Exodus 20:8-11 "Remember the Sabbath day, to keep it holy. 9 Six days you shall labor, and do all your work, 10 but the seventh day is a Sabbath to the LORD your God. On it you shall not do any work, you, or your son, or your daughter, your male servant, or your female servant, or your livestock, or the sojourner who is within your gates. 11 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 made it holy.
Jesus rose on a Sunday
o Mark 16:9 Now when he rose early on the first day of the week, he appeared first to Mary Magdalene, from whom he had cast out seven demons.
o John 20:1 Now on the first day of the week Mary Magdalene came to the tomb early, while it was still dark, and saw that the stone had been taken away from the tomb.
The early church met and did its functions on Sundays:
o John 20:19 On the evening of that day, the first day of the week, the doors being locked where the disciples were for fear of the Jews, Jesus came and stood among them and said to them, "Peace be with you."
o Acts 20:7 On the first day of the week, when we [Paul and Luke and the believers] were gathered together [in Troas] to break bread, Paul talked with them, intending to depart on the next day, and he prolonged his speech until midnight.
o 1 Cor 16:1-3 Now concerning the collection for the saints: as I directed the churches of Galatia, so you also are to do. 2 On the first day of every week, each of you is to put something aside and store it up, as he may prosper, so that there will be no collecting when I come. 3 And when I arrive, I will send those whom you accredit by letter to carry your gift to Jerusalem.
o Rev 1:9-11 I, John, your brother and partner in the tribulation and the kingdom and the patient endurance that are in Jesus, was on the island called Patmos on account of the word of God and the testimony of Jesus. 10 I was in the Spirit on the Lord's Day, and I heard behind me a loud voice like a trumpet 11 saying, "Write what you see in a book and send it to the seven churches, to Ephesus and to Smyrna and to Pergamum and to Thyatira and to Sardis and to Philadelphia and to Laodicea."
The Apostles warned Believers in Jesus against legalistic observance of the Jewish Sabbath
The celebration of the Lord's Day in memory of the resurrection of Christ dates undoubtedly from the apostolic age. The original designations of the Christian Sabbath or weekly rest-day are: “the first,” “first Sabbath” the first day of the week (Matt. 28: 1; Mark 16: 2; Luke 24: 1; John 21: 1; Acts 20: 7; 1 Cor. 16: 2), and the Lord's Day, which first occurs in Rev. 1: 10, then in Ignatius and the fathers. The Latins render it Dominicus or Dominica dies. Barnabas calls it the eighth day, in contrast to the Jewish sabbath. After Constantine the Jewish term Sabbath and the heathen term Sunday (dies Solis) were used also. In the edict of Gratian, A.d. 386, two are combined: " Solis die, quem Dominicum rite dixere majores." On the Continent of Europe Sunday has ruled out Sabbath completely; while in England, Scotland, and the United States Sabbath is used as often as the other or oftener in religious literature. The difference is characteristic of the difference in the Continental and the Anglo-American observance of the Lord's Day.
Nothing short of apostolic precedent can account for the universal religious observance in the churches of the second century. There is no dissenting voice. This custom is confirmed by the testimonies of the earliest post-apostolic writers, as:
Considering that the church was struggling into existence, and that a large number of Christians were slaves of heathen masters, we cannot expect an unbroken regularity of worship and a universal cessation of labor on Sunday until the civil government in the time of Constantine came to the help of the church and legalized (and in part even enforced) the observance of the Lord's Day. This may be the reason why the religious observance of it was not expressly enjoined by Christ and the apostles; as for similar reasons there is no prohibition of polygamy and slavery by the letter of the New Testament, although its spirit condemns these abuses, and led to their abolition...
The fathers did not regard the Christian Sunday as a continuation of, but as a substitute for, the Jewish Sabbath, and based it not so much on the fourth commandment, and the primitive rest of God in creation, to which the commandment expressly refers, as upon the resurrection of Christ and the apostolic tradition. There was a disposition to disparage the Jewish law in the zeal to prove the independent originality of Christian institutions. The same polemic interest against Judaism ruled in the paschal controversies, and made Christian Easter a moveable feast. Nevertheless, Sunday was always regarded in the ancient church as a divine institution, at least in the secondary sense, as distinct from divine ordinances in the primary sense, which were directly and positively commanded by Christ, as baptism and the Lord's Supper. Regular public worship absolutely requires a stated day of worship.
We see then that the ante-Nicene [before 325 AD] church clearly distinguished the Christian Sunday from the Jewish Sabbath, and put it on independent Christian ground. She did not fully appreciate the perpetual obligation of the fourth commandment in its substance as a weekly day of rest, rooted in the physical and moral necessities of man. This is independent of those ceremonial enactments which were intended only for the Jews and abolished by the gospel. But, on the other hand, the church took no secular liberties with the day. On the question of theatrical and other amusements she was decidedly puritanic and ascetic, and denounced them as being inconsistent on any day with the profession of a soldier of the cross. She regarded Sunday as a sacred day, as the Day of the Lord, as the weekly commemoration of his resurrection and the pentecostal effusion of the Spirit, and therefore as a day of holy joy and thanksgiving to be celebrated even before the rising sun by prayer, praise, and communion with the risen Lord and Saviour. Sunday legislation began with Constantine, and belongs to the next period.
The observance of the Sabbath among the Jewish Christians gradually ceased. Yet the Eastern church to this day marks the seventh day of the week (excepting only the Easter Sabbath) by omitting fasting, and by standing in prayer; while the Latin church, in direct opposition to Judaism, made Saturday a fast day. The controversy on this point began as early as the end of the second century. Wednesday, and especially Friday, were devoted to the weekly commemoration of the sufferings and death of the Lord, and observed as days of penance, or watch-days, and half-fasting (which lasted till three o'clock in the afternoon).