In common Christian thinking, passages such as Acts 20:7,1 Cor 16:2, and Rev 1:10 demonstrate that early believers in Jesus assembled for joint worship on Sundays. However, if we examine these texts closely, we will see that claims about the New Testament origins of Sunday worship are exaggerated.
Revelation 1:10 mentions that the writer was “caught up” and experienced his astonishing visions on the “Lord’s Day” (τῇ κυριακῇ ἡμέρᾳ). It is not clear that this phrase meant Sunday, and even if it did, this verse describes John’s unique experience, rather than Christian worship. It is true that 1 Cor 16:1-2 describes the collection of money for Jerusalem on Sundays: “Now concerning the collection for the saints, as I directed the churches of Galatia, so do you also. On the first day of every week, each one of you is to put aside and save, as he may prosper, so that no collections be made when I come.” Paul directed his disciples to collect funds on Sundays but there is no indication this was done during regular worship as a Sunday offering would be taken up today. As most traditional Jews, Paul would be reluctant to handle money on the Sabbath. So his instruction may be merely practical from his perspective.
While the above verses do not describe communal Sunday gatherings, Acts 20:7-8 does depict a meeting of Christ-followers on a Sunday: “On the first day of the week, when we were gathered together to break bread, Paul began talking to them, intending to leave the next day, and he prolonged his message until midnight. There were many lamps in the upper room where we were gathered together.” In order to interpret these verses, one must know that the inhabitants of the Roman Empire did not follow the seven-day week cycle. They had no weekends or even regularly-scheduled days off (besides the cultic holidays). The notion of a “day of rest” and the seven-day cycle was called σάββατον (sabbaton) or שׁבת (shabbat) was introduced to Romans by Jews and early Christians.
For Romans, a day began at sunrise; but for Jews, a new day already started at the sunset (Gen 1:5). Since the “week” and the “first day” are Jewish temporal references, the “first day” mentioned in Acts 20:7-8 was Saturday evening, just after sunset, which explains the need for lamps (v.8). Beyond that, the “breaking of bread” (κλάσαι ἄρτον) does not describe the Eucharist, but rather the kind of normal, communal meal that we encounter in the Gospels (cf. Matt 14:19; 15:36; 26:26; Mk 6:41; Lk 22:19; 24:30, 35).
It makes sense that the early Christ-followers met on various days of the week (including Sunday). However, the New Testament never asserts that the followers of Yeshua abandoned the traditional observance of the Sabbath or treated Sunday as their preferred alternative.