Tomato Time

But how could Beren be the son of Celegorm? Logistically, the idea is much less implausible than it might seem at first glance. Beren's mother Emeldir was a daughter of the House of Beör, whose lands of Ladros were in the northeastern part of Dorthonion and adjacent to the March of Maedhros and the Pass of Aglon, which Celegorm held with Curufin. It would be very possible for them to have met, either in the course of diplomacy, sheer chance, or the fulfillment of the military duties involved in maintaining the Siege of Angband.

And considering Celegorm's longstanding and notable association with Aredhel (herself a strong-willed huntress) it seems very possible that Emeldir the Manhearted, whose "mind was rather to fight beside her son and her husband than to flee" during the Dagor Bragollach, but

gathered together all the women and children that were left, and gave arms to those that would bear them; and she led them into the mountains that lay behind, and so by perilous paths, until they came at last with loss and misery to Brethil.

when it became clear that Dorthonion would be overrun, might be the kind of woman-- a warrior and a leader in her own right-- that Celegorm Fëanorion would be interested in. And Beren, her son -- like Elwing and Eärendil -- is shown to have talents beyond the normal scope of the Edain. These talents of Beren's revolve around the domains of woodcraft and communication with animals, both of which Celegorm-- and Oromë, his patron Vala -- are notably associated with.

Beren is noted to have "[become] the friend of birds and beasts," who "aided him, and did not betray him" during his wildly successful campaign against Morgoth as a lone outlaw, and in exchange, "from that time forth he ate no flesh nor slew any living thing that was not in the service of Morgoth." And when the Eagles come to bear him and Luthien away from Angband on the strength of the fact that

among all birds and beasts the wandering and need of Beren had been noised, and Huan himself had bidden all things watch, that they might bring him aid.

it saves his life one more time-- and Luthien's, too. This is not within the normal scope of the talents of the Edain, or the later Númenoreans, when it comes to communicating with animals. The only other character in The Silmarillion who is described as having similar talents is Celegorm, who was a hunter in Oromë's train in Valinor, and from him "got great knowledge of birds and beasts, and all their tongues he knew." Oromë also gave Huan into Celegorm's service -- variably a hound blessed by Oromë or, an even greater sign of favor, one of his maiar-- who later aided Beren and Luthien in the Quest for the Silmaril.

Considering that Celegorm is notably favored by Oromë, making Beren his son also offers a plausible alternative explanation for how Beren got past the Girdle of Melian and into Doriath. The Silmarillion, of course, claims that Eru Iluvatar intervened from outside of Arda in order to facilitate Beren meeting and marrying Luthien. But considering that Eru Iluvatar's other recorded interventions in Arda include (1) dealing with Aulë creating the Dwarves, and later awakening them, (2) awakening the Elves, (3) awakening Men, and (4) drowning Númenor, an instance of matchmaking does seem a little incongruous.

Especially since Iluvatar's intervention is by no means necessary. The Silmarillion says that once the Girdle was raised,

none thereafter could pass against [Melian's] will [...] unless one should come with a power greater than that of Melian the Maia.

Oromë, as one of the Valar, is most certainly more powerful than Melian, a Maia. And Beren passing through the Girdle was only the culmination of a longer and much more dangerous voyage, beginning when Morgoth's dominion over Dorthonion became complete and Beren was forced to flee southwards (in winter!) through the Ered Gorgoroth, the Mountains of Terror, and Nan Dungortheb, the Valley of Ungoliant,

where the sorcery of Sauron and the power of Melian came together, and horror and madness walked [...] No food for Elves or Men was there in that haunted land, but death only. That journey is not accounted least among the great deeds of Beren, but he spoke of it to no one after, lest the horror return into his mind; and none know how he found a way, and so came by paths that no Man nor Elf else ever dared to tread to the borders of Doriath.

Divine intervention seems like a very plausible reason for Beren to have survived this journey in the first place. Oromë, the Vala associated with hunting and woodcraft, who "pursu[ed] to the death the monsters and fell creatures of the kingdom of Melkor," and who surely approved of Beren's unceasing opposition of Morgoth, seems a likely source. And if Oromë's blessing was potent enough to permit Beren to survive the Ered Gorgoroth and Nan Dungortheb-- where Sauron and Melian's power clashed and created horrors-- it very plausibly could have permitted Beren to pass through the Girdle (which was held by Melian's strength alone), without requiring external intervention by Eru Iluvatar.

Could this blessing have come to Beren independent of him being a half-elf, or a son of Celegorm? Perhaps. But the Valar rarely concerned themselves with the Edain-- the legendarium treats the issue of Ulmo and Tuor largely as a special case-- and Oromë's direct intervention in Beren's life seems most plausible if Beren is at least half-elven, and even more so if he's the son of Celegorm, Oromë's favorite elf.

And there are additional thematic benefits to Beren being a half-elf of Fëanorian descent as well. To jump six thousand years into the future of Arda, Tolkien conceived of Arwen's marriage to Aragorn as the source of a final infusion of Elvish and Ainurin heritage into Middle-Earth as the Elves began to Fade. The character of this 'infusion' was of course determined by Arwen's own heritage, which combines the legacies of every known line of Valinorean and Sindarin royalty -- Ingwë through Indis; Olwë through Finarfin and Galadriel; Finwë through Finarfin and Fingolfin; Elwë/Thingol through Luthien -- except the line of Fëanor, which seems to be rather pointedly excluded.