"The Dark Fire Will Not Avail You"

[Inziladun]

Originally Posted by Legate of Amon Lanc

It is really simple if you think that the Ainur, after coming into the world and taking on material form, lost direct contact with Eru. When you are not in dialogue with someone, you can start imagining stuff about him and finding your own interpretation of his deeds/opinions/etc. (since you have no feedback, it is easy). Interpreting things you see... if Saruman or whoever was not in dialogue with Eru (or for the Istari, with Valar who gave them their mission) to "check back" with them, or to remind himself what they would really say to his situation and to what Saruman was doing, he can start finding his own excuses for what he was doing.

Also, the longer the "estrangement" from the faithful Valar, and by proxy, the One, the easier self-delusion becomes.

That is why it would have been possible for Saruman, for example, to have repented after he saw his own plans of domination quashed. Therefore, Gandalf offered him the opportunity.

With the Balrog, much longer in evil servitude, you don't see Gandalf trying to talk it out of evil; he basically just told it where to go.