Here is the MacArthur book that Platt is quoting from: The Glory of Heaven: The Truth about Heaven, Angels, and Eternal Life (2nd edition, Crossway, 2013).
In this podcast, John Piper argues against such books from Isaiah 8:19 (And when they say to you, “Inquire of the mediums and the necromancers who chirp and mutter,” should not a people inquire of their God? Should they inquire of the dead on behalf of the living?)
God’s beef with necromancy is that it belittles the sufficiency of his communication. Why would you inquire of the dead to find out what you want to know instead of inquiring of me? And if they say: Well, I have inquired of you and you didn’t tell me what I want to know. He would say: Well, that is your problem. I have told you what you need to know. You don’t need to know about such and such if I haven’t told you. And, in fact, if you go trying to inquire about such and such that I haven’t told you, you are dishonoring me. So that is the nature of the argument. And, therefore, I think the prohibition of séances and necromancy applies to this kind of thing and people ought to stop writing those books.
Here is the trailer for the film coming out on Easter that will have everyone talking about this again: