when a church has budget they hire artists. The artist puts their own style in the work. If the artist is also a secret mason, he puts a pyramid in and hopes it's fine. The people might say 'I don't like that' and they will have them remove it. A parish can have the whole place redone, paint over eerything.
Each Catholic Church is different.
The art is for the honoring of the Holy Dead.
Much of the artwork were the memes of their day.