The Two Towers by J.R.R Tolkien (Harper Collins 1991, 2007) pp. 646-652
“Will you not open your mind more clearly to me?” Aragorn asks of Gandalf and so begins a situation room briefing from the one who has a better understanding of the big picture in Middle-earth than, perhaps, anyone in the story.
“The Enemy, of course, has long known that the Ring is abroad, and that it is borne by a hobbit. He knows now the number of our company that set out from Rivendell and the kind of each one of us. But he does not yet perceive our purpose clearly.”
Sauron does not perceive the purpose of his enemies at this point of the story, nor will he do so until the very end when Frodo claims the Ring within Mount Doom itself. And at that point we learn that “the magnitude of his own folly was revealed to him in a blinding flash and all the devices of his enemies were at last laid bare”. But at this point it is all too late.
But why did the Dark Lord not even consider that it might be possible that his enemies would seek to destroy the Ring? Gandalf answers this question quite simply.
“He is in great fear, not knowing what mighty one may suddenly appear, wielding the Ring, and assailing him with war, seeking to cast him down and take his place. That we should wish to cast him down and have no one in his place is not a thought that occurs to his mind. That we should try to destroy the Ring itself has not yet entered into his darkest dream.”

It is a vital insight within The Lord of the Rings that goodness can understand evil because goodness has had to face and to overcome all that evil has to offer while evil understands nothing of goodness merely regarding it as a weak form of itself. So it was that when Frodo offered the Ring to Galadriel she replies by saying, “I do not deny that my heart has greatly desired to ask what you offer. For many long years I had pondered what I might do, should the Great Ring come into my hands”.
In order to understand goodness truly we need to think about those years of great desire and the slow formation of a character of adamant that took place during that time. Perhaps there were times within those years when Galadriel was tempted to the very limits of her endurance, perhaps as she watched the slow decay of all things around her and the rise of darkness close by her home with the Balrog in Moria and the Necromancer in Dol Guldur. Saruman could see these things too and he also desired the power that the Ring could give in order to overcome them. But while within the heart of Galadriel the desire for power lived alongside a longing to preserve beauty, goodness and truth, no such struggle took place within the heart of Saruman. He came to see the world merely in terms of strength and weakness and assumed that either Galadriel, Gandalf and Elrond were weak or ineffective or that they were secret competitors, merely hiding their desire behind a cloak of beneficence.
And what was true about Saruman was most certainly true about Sauron. Galadriel put this in these words:
“I say to you, Frodo, that even as I speak to you, I perceive the Dark Lord and know his mind, or all of his mind that concerns the Elves. And he gropes ever to see me and my thought. But still the door is closed!”

This is why Sauron is in great fear. He assumes that as the Ring has indeed been found that it is inevitable that that one of the mighty among his foes will take it and use it against him. He may be puzzled why it would appear that the Ring is in the hands of creatures as insignificant as hobbits but this aspect of the story does not seem to bother him greatly. When before the battle at the Black Gate the so called Mouth of Sauron shows the tokens that seem to denote that Frodo has been captured he does so with the words, “What use you find in them I cannot guess; but to send them as spies into Mordor is beyond even your accustomed folly.” Sauron simply assumes that the hobbits are being used in some way because that is what he would do with them.
Goodness understands evil because it has had to overcome the temptation to possess all that evil seems to be able to offer. True goodness has been formed by this inner struggle. Evil on the other hand understands nothing of this. It has not been formed by struggle. The character of Sauron, Saruman, and Gollum, too, for that matter, is not formed by inner struggle but by their being taken possession of by their desire for mastery.