Daniélou, Jean, S.J. "Chapter Fifteen: The Lord's Day." The Bible and the Liturgy." Notre Dame, IN: University of Notre Dame Press, 1956, pp. 242-261.
In contrast to a Sabbath observance, "as early in the second century, Ignatius of Antioch defined the Christian by the celebration of the kyriake" (Lord's Day) (Daniélou 1956, 242). Daniélou also observes that Pliny, in his letter to Trajan, knew that Christians gathered on a fixed day. The day of celebration, commemorating the day of resurrection, can be dated as early as the week after the resurrection. It quickly became the commemoration of the day (Daniélou 1956, 243).
Daniélou notes that a day of rest was perfectly common even in the pagan religions (Daniélou 1956, 243). In this way, the Jewish Sabbath, the pagan rest days, and the Christian Lord's Day were somewhat similar. However, the Christians quickly separated the day of rest from the day of worship, fixing Christian worship on Sunday (Daniélou 1956, 244). For a day of rest they joined with the calendar and customs of the surrounding culture. This did become easier within Roman territory when Constantine made the day of the sun, a time observed by pagans, a holiday. This rather naturally made the situation easier both for Christians and pagans (Daniélou 1956, 245).
At this point, Daniélou reminds us that the Christians saw the Sabbath as fulfilled in Christ. The Lord's Day, though it came to include rest, was not the Sabbath (Daniélou 1956, 246). The Fathers did not equate the two. The idea of a transfer of the Sabbath to the Lord's Day does appear in Origen (Contra Celsum), but the context is that the Jews, having failed to hold to the Sabbath command, are now presented with a day for worship and rest on the Lord's Day rather than the Sabbath (Daniélou 1956, 247). The fact that the Day of Resurrection was also the first day of the week, also the day of creation, was not at all lost on the Fathers. The symbolism informed a good deal of teaching (Daniélou 1956, 249). The first day of the week was recognized as the day when the work of God is taken up. It was seen as the beginning, rather than a Sabbath end of creation and work (Daniélou 1956, 251).
In addition to a day of resurrection, Daniélou observes that some of the Fathers understood the first day of creation as the time of generation of the Word (Daniélou 1956, 252). He does acknowledge the dangers of falling into a subordinationist position.
A concept of a planetary week was coming to Western thought from the East around the time of the start of Chrsitianity (Daniélou 1956, 253). In this model, the first day of the week was Sunday, the dies solis. The resemblance does not in itself seem purposeful, but by the fourth century the themes were often taken to coincide and to bear symbolic importance. Sunday was the first day of creation and the occasion for the creation of light.
From an early time, as evidenced by Barnabas and Justin, the day of the Lord was also seen as the "eighth" day (Daniélou 1956, 255). The eighth day concept appears in 2 Enoch 33:7, where it is symbolic of new creation (Daniélou 1956, 256). However, Daniélou notes the idea was never well developed in Judaism, but only in Christian thought. Christians did see this as a difference which set Christianity apart from Judaism (Daniélou 1956, 257).
Not to be outdone by orthodoxy, Daniélou notes that Gnostic thought created elaborate systems of typology for the number eight and the eighth day (Daniélou 1956, 258). He illustrates several in brief terms.