As nouns the difference between missa and massa

is that missa is (music) a mass, in the sense of a composition setting several sung parts of the liturgic service (most often chosen from the ordinary parts kyrie, gloria, credo, agnus dei and/or sanctus) to music, notably when the text in latin is used (as long universally prescribed by rome) while massa is a mass.

As a verb massa is

to mass, to sing/speak (as if) in church.