Why do we worship on Sunday?

Dear Rev. Know it all,
A friend of mine told me that Sunday Mass proves that the Catholic Church is not the church that Jesus founded because Jesus was a practicing Jew and St. Paul and St. Peter were practicing Jews and all the first Christians were practicing Jews and they would certainly have worshiped on Saturday because Saturday, the seventh day of the week is the Sabbath, not Sunday which is the first day of the week. The very concept of the week and the imposition of Sunday worship were unknown in the ancient world until the emperor Constantine created the Catholic Church and imposed Sunday as a day of worship because he was really a sun worshiper. Is this true?
Yours,
Judy Eizer

Dear Ms. Eizer,
You friend is obviously watching too much of the History Channel. Aren’t I always telling you not get your religion, or your history for that matter, from the History Channel? These days, the History Channel is mostly about Nostradamus and UFOs. The fact that the church celebrates Mass, or more properly the Eucharist, on Sunday proves that it is the most Jewish, or more properly, Israelite, church there is.
The Jewish (originally Babylonian) 7-day week was well know in Rome and Alexandria in the first century. Both cities, especially Alexandria, the empire’s largest city, had very large Jewish communities. Perhaps as much as 10% of the empire was made up of Jews and Samaritans. The seven-day week was well known as early as the 1st century and had replaced the Roman (originally Etruscan) 9-day week by sometime in the third century. By the time Constantine made it official in 321AD, the 9-day week was a thing of the past. Constantine simply recognized a useful system already in place.
Now, on to the Eucharist! Mass is a fairly recent word, late Latin, or early middle ages, I suspect. It means “the Dismissal.” The proper name in Greek and Latin for the central act of worship in the Catholic Church is “Eucharist,” a Greek word that means “Thanksgiving.”
Your friend’s first error is to say that the Jews worshiped on Saturday. They worshiped every day, Saturday being a day of increased restrictions, not necessarily of assembly. Though Jews usually go to synagogue on Saturday, they are not required to do so. The synagogue is not mentioned in the torah. It is a late development in Judaism. That the Eucharist was celebrated on the first day of the week, and not on the Sabbath, is clear from the Biblical text. Read Acts 20:7; "On the first day of the week we came together to break bread.” (the Breaking of the Bread” was an early name for the Eucharist) or 1Corinthians 16:2; On the first day of every week, each one of you should set aside a sum of money in keeping with his income, saving it up, so that when I come no collections will have to be made. Also, Apocalypse 1:10, On the Lord's Day I was in the Spirit. So, the first day of the week was the day of Christian Assembly.
The importance of Sunday becomes even clearer in the first non-Biblical Christian authors. In the “Teaching of the Twelve Apostles” (also called the “Didache”, written somewhere in Syria between 80 and 110 AD) the injunction is given: "On the Lord's Day, come together and break bread. And give thanks (offer the Eucharist), after confessing your sins that your sacrifice may be pure". St. Ignatius (around 105 AD) speaks of Christians as "no longer observing the Sabbath, but living in the observance of the Lord's Day, on which also Our Life rose again". In the Epistle of Barnabas (around 100AD) we read: "Wherefore, also, we keep the eighth day (i.e. the first of the week) with joyfulness, the day also on which Jesus rose again from the dead".
Finally, St. Cæsarius of Arles in the sixth century taught that the holy Doctors of the Church had decreed that the whole glory of the Jewish Sabbath had been transferred to Sunday, and that Christians must keep Sunday holy in the same way as the Jews had been commanded to keep holy the Sabbath Day. The observation of Sunday as a kind of Sabbath of rest was introduced gradually, but from the very beginning, the Christian community assembled and celebrated the Eucharist on Sunday, the first day of the week.
The question is not when or if this happened. It was clearly the practice of the first Christians from at least 50AD. The question is, “Why did this happen?” The answer is really very simple. The first Christians observed the Jewish synagogue and temple liturgy when they were able. They observed Sabbath. For instance, we read in Acts 16:13 On the Sabbath we went outside the city gate to the river, where we expected to find a place of prayer. Daily morning and evening prayer in the synagogues mirrored the daily morning and evening (late afternoon) sacrifices in the temple. Christians continued these observances and we still do. They are the origin of morning and evening prayer from which the Liturgy of the Hours developed. (also called the breviary or the divine office) The Jews had a very structured liturgy and here lies the problem. The first Catholics, being observant Jews, just couldn’t do some things on the Sabbath. There are 39 melakhot (forbidden things) that surround Sabbath observance, things such as lighting fires, or bearing burdens, among which was counted the carrying of money. We have already seen that the Christians collected charitable funds at their meetings. Jews are forbidden to carry money on the Sabbath. They even try not to talk about it. There is something else forbidden on the Sabbath that is even more to the point.
The regular Jewish liturgy has certain restrictions on Sabbath. Personal petitions may not be made in the synagogue liturgy and Psalm 100 (Mizmor LeTodah, the psalm for the Thanksgiving offering), is omitted from the liturgy on Sabbath even to this day by certain Jewish communities because the todah or Thanksgiving offering could not be offered on Sabbath when the temple still functioned in Jerusalem. The Thanksgiving sacrifice was forbidden because all personal petitions and prayers were forbidden in Sabbath liturgy.
There it is. The Thanksgiving Sacrifice could not be offered on Sabbath and the Eucharist is the Thanksgiving Sacrifice par excellence. The very word means Thanksgiving and, as I’ve said above, the Didache insists that the Eucharist was a true sacrifice because it must be made pure by the confession of sins. “And give thanks (offer the Eucharist), after confessing your sins that your sacrifice may be pure". The Rabbis say in the Talmud that when the Messiah comes all the sacrifices of the temple will cease except the Thanksgiving Sacrifice.
The first Christians held that Jesus was the Messiah and that he had delivered them from death. When a person was in mortal danger and was healed or rescued from danger, he needed to bring a "Thanksgiving-offering" to the temple. Were the first Christians not rescued form death by the resurrection? Would it not be reasonable to offer the Eucharist, the finest Thanksgiving Sacrifice they knew? They couldn’t offer it on Sabbath. It is notable that the Thanksgiving Sacrifice could be eaten anywhere in the city (The met in their homes for the breaking of the Bread Acts 2:46). Their assembly would have to wait for the first day of the week which was associated in their minds with Jesus’ Resurrection anyway. It was not offered in Herod’s temple, but in the temple not made by hands, the temple of living stones, the Church Assembled! In one fell swoop we see that the first Jewish Catholics were simply practicing Jewish custom by offering Mass on Sunday. It also shows that they regarded the Eucharist as a true sacrifice.
The Eucharist belonged to the temple, not to the synagogue, because it was the Sacrifice of Calvary renewed, not just a word service. Had it been simply a word service or fellowship meal, they could have and would have done it on Saturday. Those who claim that Mass is not a sacrifice, but simply a commemorative meal, and those who maintain that Saturday is the day Christians should gather are far removed from the practice of the first Christians they claim to emulate. It is the Catholic Church that preserves the unbroken chain of worship that the Lord promises in the Law of Moses. “You shall offer bread and wine and a Lamb forever”, bread and wine, become the Lamb which is Christ.
Rev. Know-it-all