The New Testament gives the local congregation final authority in matters of discipline (Matt. 18:17; 2 Cor. 2:6) and doctrine (Gal. 1). This means that there are times when the church as a whole should welcome in new members, remove members who move away, carry out church discipline, elect elders and deacons, and decide on other serious matters.
There are a couple reasons why this business should not be done in the context of a regular worship service.