Why were the disciples assembled? For a religious service? No, FOR FEAR OF THE JEWS.
"Now on the first day of the week, when the disciples came together to break bread, Paul, ready to depart the next day, spoke to them and continued his message until midnight." (Acts 20:7)
This is Saturday night. Breaking bread is a generic term used for a meal. We still use it today. This is merely fellowship after the sabbath, which ended at sunset. There is no mention of any kind of religious service. Incidentally I thought you might find Acts 20:6, the previous verse, interesting:
Act 20:6 We sailed from Philippi after the days of Unleavened Bread, and came to them at Troas within five days; and there we stayed seven days.
Interesting how Luke marks the time in a Christian holy book by citing a festival that supposedly no Christian kept.
"On the first day of the week let each one of you lay something aside, storing up as he may prosper, that there be no collections when I come." (1 Cor. 16:2)
Paul apparently isn't coming on the first day of the week since he tells them to collect goods. It's not like a Sunday pass the plate collection because here's the next verse:
1Co 16:3 When I arrive, whomever you may approve, I will send them with letters to carry your gift to Jerusalem;
Paul is taking the stuff the Corinthians collect to Jerusalam. Why? Here's why:
Act 11:28 One of them named Agabus stood up and began to indicate by the Spirit that there would certainly be a great famine all over the world. And this took place in the reign of Claudius.
Act 11:29 And in the proportion that any of the disciples had means, each of them determined to send a contribution for the relief of the brethren living in Judea.
Act 11:30 And this they did, sending it in charge of Barnabas and Saul to the elders.
There ya go. There was a famine in Judea. Paul tells each of the churches to collect food and stuff for the brethren in Jerusalem. Kind of like relief effort for hurricane Katrina or Rita.
What has happened topcat is that you look at these verses through the backwards lens of tradition and history. Tradition and history have "evolved" the sabbath from the seventh day COMMANDED and CREATED by the Lord God to the first day of the week, created by man.
After the resurrection of Jesus, when the old covenant began to pass away from the scene (Heb. 8:13), where did the apostles gather with the people and set aside the last day of the week? Please be specific.