Actually, most Jews spoke
Greek and Aramaic. They spoke Koyne Greek (translates to 'Common Greek'), which is why the gospels were originally written in Greek--so that the people could read them. There wouldn't be much point passing around scrolls when you're in the
catacombs if nobody can read it.
The reason it was in
Aramaic was probably because that's what most Jews spoke primarily. They
could speak Greek, but it was more of a second language.
Just to try to clarify that point.