For the first 300+ years, Christianity had no Bible nor legal status. Epistles and Gospels were floating around from church to church. There was the Septuagint, the Greek translation of the Old Testament (which is far older than our Old Testament and more accurately matches the Hebrew Dead Sea Scrolls). To instruct the early Christians, the men who were ordained by the apostles who would ordain others after them relied on the tradition handed down by those who walked with Jesus during his ministry on earth.
One of the most admired of these men was Ignatius. According to Orthodox tradition, he was the child that Jesus sat in the midst of the disciples when they asked, “Who is the greatest in the kingdom of heaven.” Ignatius became a disciple under John the Gospel writer and served as the bishop of Antioch after Peter and Paul before his martyrdom to the lions in Rome. En route to his death, this bishop wrote a series of letters concerning church unity and practice.
In his Epistle to the Magnesians, Ignatius gives a lesson on how Christians are to approach the Sabbath and the Lord’s Day (note: they are NOT the same):
Let us therefore no longer keep the Sabbath after the Jewish manner, and rejoice in days of idleness; for “he that does not work, let him not eat.”688 For say the [holy] oracles, “In the sweat of thy face shalt thou eat thy bread.” 689But let every one of you keep the Sabbath after a spiritual manner, rejoicing in meditation on the law, not in relaxation of the body, admiring the workmanship of God, and not eating things prepared the day before, nor using lukewarm drinks, and walking within a prescribed space, nor finding delight in dancing and plaudits which have no sense in them.690 And after the observance of the Sabbath, let every friend of Christ keep the Lord’s Day as a festival, the resurrection-day, the queen and chief of all the days [of the week].
The idea that Sunday is the “Christian Sabbath” was not taught by the first Christians nor is it taught by the first and oldest continuous expression of Christianity, the Orthodox Church. Saturday is still the Sabbath Day. It is a day of great reverence for the law of God. But, it is not a day of rest as taught by Judaism. Those who wish to work should do so. If chores have to be done, let them be done. We are to do as we wish as long as we are mindful that the Lord is the creator and sustainer of all things.
Sunday is the day Christians are to celebrate the Resurrection of Jesus. Ignatius gives no ban on labor or travel. But his words, “as a festival,” indicate that we friends of Christ are to be joyful and in celebration with one another. As ancient believers were under persecution until 325 AD, I doubt if any of them asked to have Sunday off from the job. Nevertheless, the Lord’s Day was the day to be with fellow believers and celebrate the gift of salvation.