At one point the composer tells his choirboys to sing the aria.

She would try to sing an aria, and he would react and interrupt, with such antics as falling off the bench in surprise when she hit a high note.

I have sung the arias in concerts for a long time already, and it doesn't have a big orchestra.

This allowed anyone to sing the arias themselves.

After a secco recitative, the bass sings an aria over oboe and strings.