1 Corinthians 16:2 (ESV)

2 On the first day of every week, each of you is to put something aside and store it up, as he may prosper, so that there will be no collecting when I come.

Paul does not prescribe a specific amount of what the church members should put aside. He wants each church member to contribute according to his means (as he may prosper). Each member is to put aside an amount of money on a weekly basis.

Contributions should be put aside and stored up on the first day of every week; in other words, on a Sunday. This strongly suggests that church members were not to store up their contributions at home, but that they were to bring it to the church gathering. It is there where the weekly collection was to take place. The word collection (1 Corinthians 16:1–2) itself implies that a group of people would be involved.

Since the Sunday of Christ’s resurrection, the church used this day to gather for worship (John 20:1; Acts 2:1; Acts 20:7). Christ appeared to his disciples on two consecutive Sundays (John 20:19, John 20:26). It was also on a Sunday that he poured out his Spirit (Acts 2:1). For these reasons the Sunday, or the first day of the week, soon became known as the day of the Lord (Revelation 1:10).

For the second time in the letter (see also 1 Corinthians 4:18–21) Paul speaks of his planned visit to Corinth. Probably in order to safeguard the Corinthians against embarrassment or hasty giving at the time of his visit, he tells them to finalize the collection beforehand. Christian giving should be thoughtful and regular, rather than sporadic or motivated by external pressure (see also 2 Corinthians 9:5).