with the arid plain behind me
As Eliot notes already, this line is associated with Weston's From Ritual to Romance, particularly the chapter on the Fisher King. After reading this source, the most memorable takeaway is the idea that "The Fisher King is... the very heart and centre of the whole mystery" and that he is "the essential centre of the whole cult, a being semi-divine, semi-human, standing between his people and land, and the unseen forces which control their destiny." First, I am reminded of Tiresias, who connects all the characters in TWL, which compares to the Fisher King being the center of all. Perhaps the contrast is that Tiresias spreads over a wide spectrum of characters and themes, whereas the Fisher King stays put while the wide spectrum surrounds him. Then, the idea of the King "standing between his people and land" seems to reflect line 425. If "I" am "Fishing" where the sea of fish is in front of me, "with the arid plain behind me," then "I" am essentially in between the two. Could it be that "my" "people" are compared with the fish that "I" am fishing? Can we, humans, be deemed correlated with "the Fish", whose connection "with life, renewed and sustained, is undeniable"? Perhaps Eliot is tying back the idea of humanity being part of a larger cycle of life, death, and restoration, since Weston notes that "all life comes from the water".
Another observation I have is the diction of "shore". In the first line in this last stanza, Eliot composes the image of "I" sitting "upon the shore". However, "shore" is verbalized into "shored" in line 431. What seems to be a fixed setting transitions into an action, advancing this progressive cycle that evokes the imagery of the first section of TWL. Then, the idea of "I" (Eliot? Tiresias? The Fisher King?) having "These fragments" to be "shored against my ruins", alludes to finding fortification and stability (as the verb shore is defined as to support or hold up something) in "ruins", a wasted state. Maybe Dante's "Then he vanished in the fire that defines them" and De Nerval's "the prince of Aquitaine, his tower in ruins" that precede line 431 are the "fragments" that support the narrator among such "ruins". Am "I" "the prince of Aquitaine" who is stuck in "his tower in ruins" or am "I" the one vanishing in the fire and as Dante describes "as fish glide to the bottom through the water"? Nevertheless, these identities are "shored", maybe at "shore", because the three repeats of "Shantih" that closes the poem, which Eliot says represents "The Peace which passeth understanding", convey the idea of finding peace that comes with knowledge. Though as readers we are unsure of a lot in TWL, Eliot could've experienced personal clarity and revelation throughout writing and concluding his poem. Maybe Eliot has a hold of the Salmon of Wisdom; perhaps he has tasted its "flesh that confers all knowledge", which is why we deem him as a possessor of universal knowledge that transcends boundaries. This closure of peace that proceeds understanding and knowledge could be a response to the epigraph. Though Sybil begins with the mourning of such omniscience, maybe after experiencing TWL which stands for a microcosm of daily life and its tribulations, they, representing humanity, can find peace.