It has been pointed out by many authors that the weekly cycle was observed carefully since creation. However, we do not need to go back that far. When Jesus was on the earth, he observed the Sabbath. In doing so, He, as God, confirmed the correctness of the observation of the weekly cycle since creation up to His time. Our task, then, is to confirm the maintenance of the weekly cycle since Christ. In the process, we can attach modern names to days.

Our search must take us to the earliest sources available. The Bible is of no direct help in this, since it does not use modern names for days. The only names it uses are the "preparation day", the "Sabbath", and the "first day of the week". We do not know from the Bible the names for other days of the week. In fact, from the Bible, we do not even know if such names existed. Our best inference is that they probably did not exist, since only the Sabbath is given a proper name.

One of the early heretical leaders of a church in Rome was Marcion (ca. AD 144). He prescribed many actions which we recognize as being un-Christian. His influence was widespread, and led his contemporary Epiphaneus to write that Marcion ordered his followers "to fast on Saturday justifying it in this way: Because it is the rest of the God of the Jews ... we fast in that day in order not to accomplish on that day what was ordained by the God of the Jews". (Adversus haereses 42,3,4) Since we know that the Jewish day of rest is called the Sabbath, and is also the seventh day, Epiphaneus is here equating Saturday with the Sabbath.

Pope Sylvester (AD 314-335) states: "If every Sunday is to be observed joyfully by the Christians on account of the resurrection, then every Sabbath on account of the burial is to be regarded in execration of the Jews". (quoted by Cardinal S.R.E. Humbert, Adversus Graecorum calumnias 6, PL 143, 937 1054 AD) Since the gospels record that Jesus was crucified on "the preparation day", rested in the grave on "Sabbath", and arose on the "first day of the week", then Sunday is the day on which Jesus rose. Since Sunday remains the first day of the modern week, and Saturday the last, then the Sabbath, according to Sylvester, is Saturday.

The "Apostolic Constitutions" (ca. AD 375) exhorts Christians to fast on "Friday and the Sabbath", for what the Jews did to Christ, but to "eat and make good cheer, and rejoice and be glad [on Sunday], because that the earnest of our resurrection, Christ, is risen". Again we see the Friday, Sabbath, Sunday sequence, equating Sabbath and Saturday.

Victoruinus, Bishop of Pettau (ca. AD 304) comments on the fasting just mentioned. "On the seventh day ... we are accustomed to fast rigorously that on the Lord's day we may go forth to our bread with giving thanks." (On the Creation of the World, 5, ANF VII, p342) Here we see the equation of the term "Lord's day" with Sunday.

Pope Innocent I again confirms that Sunday is the resurrection day, and therefore Saturday is the Sabbath. "We celebrate Sunday because of the venerable resurrection of our Lord Jesus Christ..." (Epistolae paschales)

The Epistle of Barnabas was written between AD 130 and 138 by an unknown author. In it we find, "it is written about the sabbath also in the Ten Words which God uttered to Moses face to face on Mount Sinai, 'and treat the sabbath of the Lord as holy'... And in six days God made the works of his hands, and ended on the seventh day, and he rested on it and made it holy ... I will make the beginning of an eighth day, that is, the beginning of another world. This is why we also observe the eighth day with rejoicing, on which Jesus also arose from the dead..." This unknown author equates the "eighth day" with the resurrection, which occurred on the first day of the week. He also identifies the Sabbath as the "seventh day", or the day before the resurrection. This celebration of resurrection again shows that the Sabbath is Saturday.

Justin Martyr (ca. AD 138-161) states, "On the day which is called Sunday, we have a common assembly ... and the memoirs of the Apostles or the writings of the Prophets are read... Sunday, indeed, is the day on which we hold our common assembly because ... our Saviour Jesus Christ arose from the dead on that day..." (I Apology 67,3-7) Once again, we find the day of the resurrection identified as Sunday, and, by the sequence in the gospels, the Sabbath has to be Saturday.

It would be possible to quote many more early writers to confirm the identification of Sunday as the first day of the week and Sabbath as the seventh. To continue in such a manner would serve only to bore the reader. We can say without hesitation that the identification of the day of the week identified as the Sabbath cannot be more conclusive. No question whatever exists about this fact. No historian, whether religious or secular, disputes the fact that the Sabbath observed by Christ is Saturday. Likewise, there is no debate whatever that the day was considered to begin as sundown and end at the next sundown. As Moses recorded in the creation story:

5 And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day. Gen 1:5

All that we have discovered is confirmed by the testimony of millions of Jews who over two millennsia since Christ have zealously observed the Sabbath. Dispersed throughout the world, they all keep the same day. And when they assemble, even though there may be disputes on the proper way to observe it, there is never a dispute on when to observe Shabbat. It begins Friday night at sundown and ends Saturday night at sundown. No other single fact of history can claim the degree of certainty of the Sabbath.