Section 7. Every incorporated religious society shall hold an annual meeting at such time as it shall prescribe by its by-laws, and, if the by-laws do not otherwise provide, at a place appointed by its assessors or standing committee; and at such meeting it shall choose a moderator, clerk, a standing committee or two or more assessors, a treasurer, a collector, and such other officers as it may think necessary, all of whom, except the moderator, shall, except as otherwise provided in this chapter, hold office until the next annual meeting and until their successors are qualified. Vacancies in said offices may be filled at any legal meeting.