Why did Sauron fear Aragons coronation?

[cellurdur]

Well Sauron has a great deal of hatred for Luthien's descedants as a whole. This is further increased by the Numenoreans stopping him in the Second Age. More fuel is added to the fire when the Numenoreans give him a humiliating defeat under Ar-pharazon. Then Elendil makes the last alliance and plays a big part in personally killing his body. Lastly to add insult to the wound Isildur takes his ring. So purely from a personal point he would be angry to find out that a descendant of Isildur still lived.

The other thing that would greatly worry him is the Heir of Isildur claiming the One Ring. Technically Aragorn has a legal right to the ring, which even Frodo acknowledges at the Council of Elrond. Whilst Aragorn has no possible hope of ever defeating Sauron in a personal battle, there is a chance he could unite the armies of the West against Sauron. He may even be able to gain the Black Numenoreans to his side. With such military power, just like the Numenoreans did, Aragorn could defeat Sauron's armies.

The last reason is that it is still a huge boost for the men of Gondor and strikes fear into the orcs. As Boromir put it the 'sword of Elendil would be a help beyond hope.' Similarly I think it would be a huge blow to the elves to see Narsil reforged.

[Arathorn111]

I considered Aragorn himself and the sword of Elendil as great enemies of Sauron, however I felt that that was more dangerous to Sauron himself than to his armies. Of course it would cause fear among his armies but the differnence between Aragorn as king and Aragorn as "simply" the heir of Elendil would be small. However the stoming of Minas Tirith might just as well be to stop Aragorn from taking command of Gondors armies.

[Zigûr]

Yes this would be a classic case of where the film attributes significance to the wrong things for no essential narrative reason, which I think is one of the major pieces of evidence that the screenwriters literally didn't understand the words on the page. Sauron feared Aragorn and the Sword of Elendil mostly because he thought that Aragorn had the Ring - the Heir of Elendil with the Ring might be a formidable opponent militarily.

[Galadriel55]

I think that a big part of Sauron's fear after the Palantir "conversation" was that he wat defeated in a battle of wills/minds by Aragorn. If being the heir of Isildur, a charismatic leader of Numenorian descent, and owner of Anduril and potentially of the Ring is not enough, this little trick does it. I imagine Sauron was seriously freaking out after a "mere mortal" beat him like that in his own field.

[Inziladun]

One thing I find curious that may bear on this is Aragorn's statement to Frodo on their meeting at Bree.

'I did not intend to tell you all about myself at once. I had to study you first, and make sure of you. The Enemy has set traps for me before now.'

That suggests that Sauron was worried enough about the idea that an Heir of Isildur remained to have in some way been looking for evidence of such a person. Aragorn, of course, does not elaborate on the "traps", but it says something that even before the War of the Ring the Heir of Isildur was on Sauron's mind.

[Aiwendil]

Originally Posted by Inziladun

That suggests that Sauron was worried enough about the idea that an Heir of Isildur remained to have in some way been looking for evidence of such a person. Aragorn, of course, does not elaborate on the "traps", but it says something that even before the War of the Ring the Heir of Isildur was on Sauron's mind.

Possibly. But Aragorn was also the Chieftain of the Rangers; and even if Sauron had no idea that an heir of Isildur was alive, he must have been aware of the existence of the Rangers of Arnor. So it may be that the traps Aragorn refers to were set merely against the commander of the northern Dunedain, with no particular thought that he might be a claimant to Isildur's throne.

[Inziladun]

Originally Posted by Aiwendil

Possibly. But Aragorn was also the Chieftain of the Rangers; and even if Sauron had no idea that an heir of Isildur was alive, he must have been aware of the existence of the Rangers of Arnor. So it may be that the traps Aragorn refers to were set merely against the commander of the northern Dunedain, with no particular thought that he might be a claimant to Isildur's throne.

Would Sauron really have been that concerned about the Rangers, though? It doesn't look like he had any regard for Eriador in the Third Age, until he learned that was where his Ring had probably been taken. And if he or his servants knew of the Rangers, he should have observed they were guarding the Shire, and he shouldn't have been so clueless either about the location of Hobbits there.