The Treason of Isengard: Eru's Plan?

Originally Posted by Nilpaurion Felagund

But what role, exactly, does God play in your suicide? He just knows it. He won't stop you if you really want to do it. As I said, you are other from God. Otherwise, he'd be better off playing with Lego figures.

God knows what we'll do, but it is we who actually go there.

Or, to quote the phantom on another thread (on how Eru's omniscience and free will can co-exist):

I think you were drifting off the point of the original question here a little. Eru sent Saruman as leader of the Istari to unite the free people of ME against Sauron due to the crisis situation that was developing. He was sent with a specific reason, to perform this task together with the rest of the Order. He was, like Gandalf, forced to accept special conditions on his physical form & demonstration of his true power before being allowed to come to ME.

So Eru, after going through these things with the Istari, probably would not have known for sure of the true designs of Saruman (or why on earth send him to ME ahead of others in his realm?), but I guess that (a bit like, say Galadriel with Boromir) Eru would have suspected that something was not quite right from the beginning but could not perhaps pinpoint exactly what it was or what was going to happen & had no choice but to send Saruman & put faith in him.