Why do Christians worship on Sunday?
It's a simple question and there are a few reasons.
Here are three basic reasons why Christians assemble together to worship on Sunday.
Reason #1: Christians celebrate their belief that Jesus was resurrected from the dead on the first day of the week.
1 On the first day of the week, very early in the morning, the women took the spices they had prepared and went to the tomb. 2 They found the stone rolled away from the tomb, 3 but when they entered, they did not find the body of the Lord Jesus. 4 While they were wondering about this, suddenly two men in clothes that gleamed like lightning stood beside them. 5 In their fright the women bowed down with their faces to the ground, but the men said to them, “Why do you look for the living among the dead? 6 He is not here; he has risen! Remember how he told you, while he was still with you in Galilee: 7 ‘The Son of Man must be delivered over to the hands of sinners, be crucified and on the third day be raised again.’ ” 8 Then they remembered his words.
(Luke 24:1-8 NIV)
The resurrection of Jesus is a cornerstone of Christianity.
The apostle Paul wrote the following to the Corinthian Christians:
12 But if it is preached that Christ has been raised from the dead, how can some of you say that there is no resurrection of the dead? 13 If there is no resurrection of the dead, then not even Christ has been raised. 14 And if Christ has not been raised, our preaching is useless and so is your faith. 15 More than that, we are then found to be false witnesses about God, for we have testified about God that he raised Christ from the dead. But he did not raise him if in fact the dead are not raised. 16 For if the dead are not raised, then Christ has not been raised either. 17 And if Christ has not been raised, your faith is futile; you are still in your sins. 18 Then those also who have fallen asleep in Christ are lost. 19 If only for this life we have hope in Christ, we are of all people most to be pitied.
20 But Christ has indeed been raised from the dead, the firstfruits of those who have fallen asleep.
(1 Cor. 15:12-20 NIV)
On the night before Jesus was crucified, He established a memorial for His disciples to remember Him.
Christians refer to this memorial as The Lord's Supper, the Eucharist, and/or communion. (See Matt. 26:26-29; Mark 14:17-25; Luke 22:14-23.)
Many Christians gather each Sunday to observe this memorial in a time of somber reflection and celebration of Jesus' death and resurrection.
The early Christians often spoke of Sunday as an "eighth day" (in reference to the Genesis creation account), for on that day GOD made a new creation—resurrected humans.
"I will make a beginning of the eighth day, that is, a beginning of another world. For that reason, also, we keep the eighth day with joyfulness, the day also on which Jesus rose again from the dead."
—Barnabas (c. 70-130 A.D.)
"Our Lord Jesus Christ rose from the dead on the first day after the Sabbath. Although the first day after the Sabbath remains the first of all the days, it is nevertheless also called the eigth."
—Justin Martyr (c. 160 A.D.)
"Concerning the observance of the eighth day in the Jewish circumcision of the flesh, a sacrament was given beforehand in shadow and in usage. But when Christ came, it was fulfilled in truth. For the eighth day (that is, the first day after the Sabbath) was to be that day on which the Lord would rise again, enliven us, and give us the circumcision of the spirit. The eighth day (that is, the first day after the Sabbath), the Lord's day, was foreshadowed.
—Cyprian (c. 250 A.D.)
From very early in the Christian era, Sunday became known as "the Lord's Day." Many Christians base this association upon Rev. 1:10, believing the apostle John was referring to Sunday.
Reason #2: Christians assemble on Sundays because the New Testament indicates this was a practice of the early church.
Acts 20 shows that the Christians in Troas once met on Sunday, as Paul was passing through on his way to Jerusalem. The text reads:
6 But we sailed from Philippi after the Festival of Unleavened Bread, and five days later joined the others at Troas, where we stayed seven days.
7 On the first day of the week we came together to break bread. Paul spoke to the people and, because he intended to leave the next day, kept on talking until midnight. 8 There were many lamps in the upstairs room where we were meeting. 9 Seated in a window was a young man named Eutychus, who was sinking into a deep sleep as Paul talked on and on. When he was sound asleep, he fell to the ground from the third story and was picked up dead. 10 Paul went down, threw himself on the young man and put his arms around him. “Don’t be alarmed,” he said. “He’s alive!” 11 Then he went upstairs again and broke bread and ate. After talking until daylight, he left. 12 The people took the young man home alive and were greatly comforted.
(Acts 20:6-12 NIV)
Similarly, in the letter known as 1 Corinthians, Paul seems to allude to the Corinthians' practice of Sunday assemblies when he says:
1 Now about the collection for the Lord’s people: Do what I told the Galatian churches to do. 2 On the first day of every week, each one of you should set aside a sum of money in keeping with your income, saving it up, so that when I come no collections will have to be made. 3 Then, when I arrive, I will give letters of introduction to the men you approve and send them with your gift to Jerusalem. 4 If it seems advisable for me to go also, they will accompany me.
(1 Cor. 16:1-4 NIV)
Many Christians conclude, based on these texts, that Sunday is the day that GOD intends for Christians to meet together for public worship.
Reason #3: Sunday church assemblies are a tradition that can be traced back to the first century.
Perhaps the biggest reason why Christians regularly assemble on Sundays to worship is because it's tradition.
The early Christians met together frequently—as often as daily (see Acts 2:46).
Early, post-New Testament writings encourage daily assemblies with Christians.
"Every day, you should seek out the faces of the saints, by word examining them and going to exhort them, mediating how to save a soul by the word. Or else, by your hands, you should labor for the redemption of your sins. You shall not hesitate to give, nor murmur when you give."
—Barnabas (c. 70-130 A.D.)
"Every day, seek out the faces of the saints, so that you may be refreshed by their words."
—The Didache (c. 80-140 A.D.)
Other early Christian writings specifically mention Sunday as the time of regular Christian assemblies:
"And on the day called Sunday, all who live in the cities or in the country gather together to one place. And the memoirs of the apostles or the writings of the prophets are read, as long as time permits. Then, when the reader has ceased, the president verbally instructs us and exhorts us to imitate these good things. Then we all rise together and pray. And, as we said before, when our prayer is ended, bread and wine and water are brought. Then, the president in like manner offers prayers and thanksgivings, according to his ability. And the people assent, saying "Amen." Then, [the Eucharist] is distributed to everyone, and everyone participates in [the bread and wine], over which thanks has been given. And a portion of it is sent by the deacons to those who are absent.
—Justin Martyr (c. 160 A.D.)
Significant evidence exists that daily assemblies remained a practice among some Christians for centuries, with decreasing frequency.
In his third volume of the series The History of the Christian Church (covering 311-600 A.D.), 19th century historian Philip Schaff writes:
The Eucharist was celebrated daily, or at least every Sunday. The people were exhorted to frequent communion, especially on the high festivals. In North Africa some communed every day, others every Sunday, others still less frequently. Augustine leaves this to the needs of every believer, but says in one place: “The Eucharist is our daily bread.” The daily communion was connected with the current mystical interpretation of the fourth petition in the Lord’s Prayer. Basil communed four times in the week. Gennadius of Massilia commends at least weekly communion. In the East it seems to have been the custom, after the fourth century, to commune only once a year, or on great occasions. Chrysostom often complains of the indifference of those who come to church only to hear the sermon, or who attend the eucharistic sacrifice, but do not commune. One of his allusions to this neglect we have already quoted. Some later councils threatened all laymen with excommunication, who did not commune at least on Christmas, Easter, and Pentecost.
In time, the regular practice of daily Christian assemblies became less and less common, being replaced with regular Sunday assemblies.
I feel compelled to add some closing comments.
I have attempted to answer the spirit of the question as to why Christians assemble on Sunday.
Yet, the wording of the question reflects an inaccurate understanding of biblical worship that leads us to errant thinking.
Under the new covenant, Christian worship is an individual activity—something that may be done while by ourselves or in the presence of others.
It is crucial that we recognize that GOD looks at us individually to assess our worship (or lack thereof).
Sitting through a church assembly does not inherently mean one has worshiped GOD. Nor are church assemblies the extent to which a person worships GOD.
Avoid the mistake of thinking that "worship" implies "church." It does not.
Go here to read more about the biblical meaning of worship.