Oaths in The Silmarillion

[Finwe]

I'm curious if Tolkien ever expressed what the punishment for breaking the Oath of Feanor would have been. In LOTR, the Army of the Dead are punished in that their souls aren't allowed to depart from the world upon death, but for Elves like Maedhros and Maglor, who seemingly wished to repent of their oath, that's going to be their fate regardless.

I've always been curious as to why the eldest sons of Feanor were unable to repent. Oaths are obviously very sacred in Arda, but so also is life. I can kinda, sorta understand being outnumbered and talked into attacking Doriath and the Havens of Sirion by their brothers, who are very eager to fulfill their oath, but once the brothers are killed in the attack, what prompts them to steal the silmarils from Eonwe? If there is some sort of spiritual punishment levied by Eru for oathbreaking, do Maedhros and Maglor truly believe it would be worse than the punishment for kinslaying and murder?

I've always thought it was a father-son thing, where the brothers wanted to honor the memory of their slain father by finishing what he started at all costs, but upon Maedhros's rescue from Thangorodrim, he basically spends the remainder of the First Age repenting of the atrocities, he, his father, and brothers have committed. Maglor especially seems to have completely broken any hold the oath had on his will. Perhaps not coincidentally, he's the only brother to survive, albeit his fate is less than peachy. I'm rambling, so I'll stop now.

 

[Hamfast Gamgee]

Maybe they might have said, yes we swore an Oath but we didn't know quite what we were doing it was stupid we aren't committing Elven schism over it any more!

 

[Voronwë_the_Faithful]

Even in the watered-down version included in the published Silmarillion it states clearly what would happen to them if they broke the oath:

"They swore an oath which none shall break, and none should take, by the name even of Ilúvatar, calling the Everlasting Dark upon them if they kept it not.

In the actual words of the oath:

"Our word hear thou,
Eru Allfather! To the everlasting
Darkness doom us if our deed faileth."

 

[Radhruin]

This has surely been discussed, but is this oath somewhat akin to the fallen angels in the Christian Tradition? In the vein of the angels being "given everything", but rejecting it? Being different from us mere mortals who have the ability to seek, but are not *given* the knowledge and thus have more wiggle room to choose or reject?