Given the fact that everything about God's Word was specifically inspired by its Author, it is appropriate that this important phrase, "the first day of the week," occurs exactly eight times in the Bible. The first six of these (Matthew 28:1; Mark 16:2, 9; Luke 24:1; John 20:1, 19) all stress the fact that it was on this day that the greatest event in history (since the creation) had taken place. The creation of the universe had taken place on the first day of the week, and now its Creator had conquered sin and death itself on that day. In the Bible, of course, the number "seven" represents completeness, so "eight" represents a new beginning--a new creation, a resurrection.
The last two references tell us just how the early Christians remembered this day. Our text verse tells us this was a day on which the disciples assembled together, had a preaching service, and then "broke bread." This was not a special assembly called just for Paul, for he had already been waiting there six days (see previous verse). This was about 25 years after the resurrection itself and the Jewish believers were evidently still observing the seventh day as a rest day, but then they also observed the first day of the week as the time to commemorate the Lord's death in "breaking of bread" to celebrate His resurrection, and especially to hear the preaching of His Word. The final reference tells us one other vital thing they did: "Upon the first day of the week let every one of you lay by him in store, as God hath prospered him" (1 Corinthians 16:2). The first day of the week should always be a time of remembering Him in these joyful ways, for He is our living Lord and Savior. HMM http://www.icr.org/article/5954/