Why are communion motet logistics evidently so difficult?

It's Easter.  There are a kerfillion people in the church.  Communion is probably going to take kind of a while.  You know what's not your friend here?

A short motet.

Even two short motets will not do it.  You have to fill a lot of time.  Fortunately, literally centuries of composers have built an arsenal of ecclesiastical music, which includes a large number of pieces appropriate for the situation, some of which are quite long.  Or you can plan for about six short ones, and cut them if there's suddenly a rash of Easter truancy.

Your organist is not that good at improvisation, so please save us.