An excerpt from C.S. Lewis's book, "On Stories: And Other Essays on Literature." 1966. C.S. Lewis Pte Ltd. Pg. 24-25.
The final challenge and climax of The Lord of the Rings took place in the Chambers of Fire in Mount Doom. There Frodo faced both the baleful influence of the Enemy and the cataclysmic completion of his task. The quest was ultimately achieved, but through an unanticipated series of events.An excerpt from "New Light on the Illumination of Grendel's Mere," by Christopher Abram. JEGP, Journal of English and Germanic Philology, Volume 109, Number 2, April 2010, pp. 198-216. Pg. 200.
Descents of this type have an important role in myth, where they often provide important turning points. Sometimes they consist of a journey by a living hero into the underworld to obtain counsel or rescue the dead. (The counsel is usually oracular and the attempt at rescuing the dead is usually unsuccessful.) The descent sequences in myth are almost always pervaded by an unreal, dreamlike quality. One of the most curious, with which Tolkien was well-acquainted, is the descent by Beowulf into the lake of monsters to kill Grendel's mother. Beowulf descended through the water for hours before reaching the bottom and engaging the monster in battle. This journey is far more unreal than those into a merely subterranean underworld. The whole sequence is impossible, even to the gushing of hot blood from the body of the long-dead Grendel. However, immediately after Beowulf returned to shore, he re-entered the world of reality. His companions were suddenly concerned with practical problems, such as the transportation of Beowulf's armor and of Grendel's huge head. The same sense of unreality is present in Tolkien's descent sequences, as is the subsequent return to practical reality after the achievement of an important goal.
According to these interpretations, therefore, Beowulf’s monstrous adversaries dwell in an infernal landscape, or in hell itself: their abode is congruous with the poem’s descriptions of Grendel as a feond on helle (“fiend in hell”), helle hæfton (788a: “slave of hell”), and helle gast (“spirit of hell”).The demonic nature of the Grendelkin is unambiguous, and it is one of the most explicit signs of the poet’s Christian perspective on his material, an example of what Craig R. Davis identifies as his application to the narrative of “the moral schemes of Christian sacred history.”An excerpt from John F. Vickrey's book, "Beowulf and the Illusion of History." 2009. Associated University Presses: Cranbury, NJ. Pg. 39.
But the Beowulf-poet has (to quote Marijane Osborn) a double perspective on his story, two frames of reference—“one heroic and one cosmic. The former aligns us, the audience, with the native Germanic world within the poem, while the latter aligns us with the Christian world of the poet.”11 Within the poet’s imaginative reconstruction of the worldview of Germanic legends and their heroes, Hrothgar might recognize the fyr on flode as a niðwundor, but he would not equate it with hellfire; when Beowulf dives into the mere, the character can have no knowledge that his harrowing journey will take him into hell itself.
As we have noted, the very folktale that underlies the Grendelkin episodes in Beowulf concerns, sooner or later, a descent into the underworld, and the hero's motive in some of the Scandinavian analogues to Beowulf's descent into the mere (for instance, Grettir's venture into the howe of Kar the Old) is certainly to get hold of the monster's treasure. Both Sigemund and Heremod are spoken of, apparently, as persons with whom Beowulf himself, who has just slain the monster Grendel, is to be compared or contrasted. There is a grain of truth in Whitelock's remark that the poet did not wish to put his hero "on a level with the characters of heroic legend." Part of this contrast might be that Heremod as well as Sigemund sought out monsters to despoil them, whereas Beowulf sought out Grendel's lair only to avenge Æschere and to lay the ghost of Grendel. . . Both the first and second allusions to Heremod imply a contrast between Heremod and Beowulf, and the contrast is the more pointed if it is seen that their foes were of the same sort. Whereas Beowulf has triumphed over the Grendelkin because he applied his strength with wisdom, Heremod, we might suppose, perished mid eotenum 'among giants' because rapacity brought his strength to ruin.