In 1 Corinthians 16:1-3, Paul, the apostle, offers guidance to the churches in Galatia about gathering funds for the saints in Jerusalem who were facing hardship. He encourages them to set aside a donation at home on the first day of the week, what they could afford. The idea was to accumulate these donations until Paul could send out messengers to carry them to Jerusalem.
It’s vital to recognise that this passage doesn’t indicate any religious meeting or the collection occurring during a Sunday church service. The term “lay something aside” suggests saving up at home. This interpretation is even accepted by those who promote worship on Sundays.
The reason Paul pointed out the first day of the week was probably because his letter would’ve been read to the congregation on the Sabbath when they were gathered for worship. The next day, the first day of the week, would therefore have been a practical opportunity for them to collect and set aside their donations.
Based on this reference to the first day of the week, it’s clear that there wasn’t any change in religious practice or replacement of Sabbath with Sunday worship. Paul’s focus was on encouraging the churches to show their support and gratitude to the saints in Jerusalem who were struggling, underlining the significance of both spiritual and material assistance.