That's a good one. I was thinking of OT warnings against speaking with the dead or other ceremonies for the dead. When the Lord says to do A and B and you decide to do A, B, C, D, E, and F, you are creating religion. Man has a very nasty habit of doing that as the bible says over and over.
God is rather clear throughout the Old Testament about not communicating with the dead. He was also rather clear about not incorporating pagan worship practices in the worship of Him. Catholics have ignored all of that.