Do you have a reference for where Benjamin wrote about this? I found this excerpt from "Art in the Age of Mechanical Reproduction": "With the emancipation of the various art practices from ritual go increasing opportunities for the exhibition of their products. It is easier to exhibit a portrait bust that can be sent here and there than to exhibit the statue of a divinity that has its fixed place in the interior of a temple. The same holds for the painting as against the mosaic or fresco that preceded it."

But wasn't sure if this was exactly what you were referencing, or some other piece.