Some Mardi Gras, eh cher? Dull and depressing as hell if you ask me. Clearly Herman Melville had never heard of Professor Longhair or the Wild Tchoupitoulas when he described, in the previous Canto, The Night Ride of Clarel and his fellow pilgrims in the Holy Land on Shrove Tuesday. "Throw me something, Mister!" Too late, sorry.
https://en.wikisource.org/wiki/Clarel/Part_4/Canto_29
As there depicted, carnival is for clodhoppers (rustic laborers or "hinds") and the party is already over. "The Night Ride" found young Clarel, the wandering divinity student and hero of Melville's poem, journeying from Bethlehem back to Jerusalem and trying to decide what to do with the rest of his life. A Crossroads moment, figuratively speaking. Which of two callings or paths to take: the higher, lonelier path of unswerving devotion to God; or the more common and accessible path to earthly happiness in the enjoyment of a more domestic sort of bliss with wife and family? Clarel chooses Ruth, deciding to embrace real life with his fiancée, rather than a life of monkish austerity in pursuit of some impossibly spiritual ideal of ultimate Truth. But the cleric (and prig, still?) in him remains vaguely bothered by the thought (lately personified in the Prince-like Lyonese aka Prodigal) that his decision to embrace real life and Ruth could be less-than-nobly motivated by natural stirrings of sexual desire i.e. lust.
Clarel has just decided in favor of Ruth when he and his remaining companions (chiefly his fellow Americans Rolfe and Vine, plus Derwent the amiable Anglican priest) reach The Valley of Decision.
https://en.wikisource.org/wiki/Clarel/Part_4/Canto_30
The "Decision" communicated here is different, and absolutely not the one Clarel wanted or expected.
Where are we anyway?

From John Kitto, Physical Geography of the Holy Land (London, 1848); also The Mountains, Valleys, and Rivers of the Holy Land (London, 1866) pages 227-8:
The most extensive and important of these valleys is that which lies east of the city—between it and the Mount of Olives. This is the VALLEY OF JEHOSHAPHAT. It is rather more than a mile in length, but narrow, as there are few places in which its breadth exceeds 200 yards. This is that memorable valley so often mentioned under different names by the sacred historians and prophets; and which is sanctified in the memories of men afar off by the knowledge that its soil is replete with the dust of thousands of holy and venerable personages; and has been moistened by the tears of the prophets and the blood of the saints. Who knows not, also, that this valley was often traversed by David, or by "the Son of Man," whenever the record of their griefs bears witness that they crossed the brook of Kedron, or ascended Mount Olivet; or that it is the peculiar and awful distinction of this valley, that Jews, Mohammedans, and the mass of Christians, live and die in the persuasion that this is "the Valley of Decision,”—the valley to which all the nations shall be gathered in the great and terrible day of final judgment.https://books.google.com/books?id=NTpkAAAAcAAJ&pg=PA227&dq#v=onepage&q&f=false
Most sacred ground then, as burial place and prophesied "Dale / Of Doom, God's last assizes" (Clarel Part 4 Canto 30, lines 116-7).
Descending from Bethlehem, Clarel and company interrupt a double burial, conducted for safety's sake in the dark of night "near the place / Of Hebrew graves." Clarel learns to his horror that the bodies being buried are those of Ruth and her mother Agar. They died, as one of the group informs him, of fever or grief over the death of Ruth's father Nathan (killed by Arabs before Clarel left Jerusalem).
I suppose there's no getting around the feeling expressed by many commentators that the deaths of Ruth and Agar too conveniently resolve the narrative problem of fleshing out a pretty yet flimsy love story. In terms of narrative structure, Clarel's attachment to the daughter of Nathan and Agar frames CLAREL, but here as in other "books of talk" (John Wenke's apt expression in Melville's Muse), for substance Melville prizes nothing more than traveling and conversing. Dialogue seems to be the whole point, frequently.
Nevertheless. To give Melville his due here, we might look at a few places where he really brings it as creative writer and versifier. What I most like is how totally and thoroughly committed he becomes to visualizing scene, motive, action. For dramatic effect, which here in Part 4 Canto 30 especially means intensifying the pathos. It begins with a short but pleasant daydream of the warm welcome awaiting in Jerusalem, "door-post wreathed" at the inn. After six lines of imaginary "cheer," negative thoughts counter this early optimism. Clarel now feels the tremors of a coming earthquake, prefiguring the shock he will get when identifying the dead body of Ruth. His thoughts turn dark and fearful, foreboding and self-recriminating. Maybe Ruth never got that stupid letter he wrote her before his departure. He blames himself, rightly but way too late, for abandoning Ruth in her emotional distress:
"To leave her, leave her in grief's smart:Though belated and practically useless, such "Vain goadings" as these attest to Clarel's revived love and help motivate him to speed up his return. Melville visualizes him thus in the verse, graphically, leaning forward on his horse and pressing ahead to Ruth with renewed energy:
"With knee
And below, from the Pictorial Journey Through the Holy Land (London, 1867) page 65:

Dear Scott,
Well done and thanks for the great travel sources. A stranger to Palestine might ask, “who decides in this Valley of Decision? Every one of us knows his body will eventually stop breathing and rot away. There are many theories to choose from for what happens to our "I am being" after death. Why would anyone, in particular, be judged after death since both joy and suffering require a body and the soul comes from God?
For the believers in a Valley of Decision, they have a God who has taken the sting out of death by promising a Paradise for those who follow his will, He will decide from “Jews, Mohammedans, and the mass of Christians, [who] live and die in the persuasion that this is ‘the Valley of Decision, to which all the nations shall be gathered in the great and terrible day of final judgment.”
The poet has prepared his readers by illustrating other decision-makers as the cause of suffering or redemption without projecting it into the afterlife. A very direct example is another poem The Age of the Antonines.
“The sting was not dreamed to be taken from death,
No Paradise pledged or sought,
But they reasoned of fate at the flowing feast,
Nor stifled the fluent thought,
We sham, we shuffle while faith declines--
They were frank in the Age of the Antonines.”
In the Greek and Roman Ages, morality/ethics were considered innate in man and children learned from examples. Socrates demonstrated with an illiterate slave that virtues were universally known and recognized. The gods were seen as the source of feelings (Eros’ arrow as love) and not morality. They needed to be appeased or thanked for good feelings and driving away the bad.
The influence of the Judeo-Christian God changed the Roman world by creating a belief that after death one would find immortal justice. A God who could save one from one’s own errors created a belief that death did not terminate one’s rewards or punishments. Not unlike an elegant con game the sufferer could give up the life he has for the reward promised in the Word with only his faith as a guarantee. This made a Martyr's role easier because suffering had a future reward.
For Clarel the choice of martyr for his suffering is symbolized
The Martyr's port is won--
Stephen's; harsh grates the bolt withdrawn
And, over Olivet, comes on
Ash Wednesday” indeed.
Hardeman