What effect do you think new, massive structures, especially churches, had on the size and subject matter of artwork commissioned to fill them?

Imagine you are commissioned to make a painting: you would probably want people to be impressed by your work.

If your painting were to be hung next to very beautiful pieces of art, the painting might "dissapear" among them, so your painting would have to be more exceptional and attention-drawing.

So the effect was that art became more "attention-drawing", more expressive for example, and that it also became bigger to be more visible.