David's Well inspires Clarel to reflect on fundamental questions. Given worldly baseness, can you really keep true to the dreams of youth? In different formulations (as William H. Shurr observed in The Mystery of Iniquity, explicating "The Enthusiast") this theme preoccupied Melville over many decades of thinking and writing. Here at the well Melville dumps his favorite antitheses on Clarel. Body and soul, physical and metaphysical, philosophy and economics, spirit and dust. If you would live by the Holy Spirit, examining life and pursuing Truth, "how mix with tempers keen / And narrow like the knife?" Personified, that knife-sharp dude might be somebody like the traveling preacher in Rip Van Winkle's Lilac:
"a gaunt, hatchet-faced, stony-eyed individual, with a grey sort of salted complexion like that of a dried codfish, jogging by on a lank white horse."Melville's worldly sharpers are not always so ugly, however. In manuscript, the second Camoens poem After offers a handsomer version, "fair in face."
https://books.google.com/books?id=X201AQAAMAAJ&pg=PA414&dq#v=onepage&q&f=false
Prompted by John Gretchko to read canto 28 more closely, I noticed how the questioning effectually introduces the Russian. Clarel wonders how to interact with materialists possessed of knife-like personalities, keen and narrow.
Lo and behold, here comes one now! As if on cue, the Russian emerges from the bushes. Orchard, rather, "from a vineyard nigh." (Trouble in Paradise?)
In conversation, the tall strong and handsome Russian makes pointed comments while questioning Clarel about the Prodigal. Flashing a "meaning smile," the Russian has a way of insinuating with leading questions.
And ignoring the answer:
Not marking herehttps://books.google.com/books?id=BvRDAQAAMAAJ&pg=PA549&lpg#v=onepage&q&f=false
Clarel has just caught himself misquoting the Prodigal. Misremembering and misreporting, specifically by imputing to his late cell-mate a blasphemous view of the Bible as a kind of "Runic spell." With admirable honesty, Clarel admits his mistake and confesses the word Runic was wrong.
But our Russian misses the point of Clarel's self-upbraiding. Why? Because he's on a mission, "full of his own thoughts in clew." Self-absorbed, with his own agenda, our Russian holds fast to his own thoughts like Theseus with a ball of yarn, following the thread to get in and hopefully out of the Labyrinth.

Being impressible, Clarel makes a literal and figurative "leap" (line 125) in accepting the Russian's confident, emphatic identification of the Prodigal as "a Jew!" Less certain, however, Clarel begins to "demur" while the Russian presses on to prove his theory by analogy with branded sheep that never can rub off their distinguishing earmark. Through a combination of bluster, fantasy, psychological manipulation, projection, and questionable analogies the Russian magically turns guess into fact:
"My late surmise is surety now,"
Hahahaha.
About the Easter ending, Melville made it happen in a year when the holy day was the same for both churches, Roman Catholic and Greek Orthodox. Looking ahead to canto 33, I see Melville so stipulates:
"And when the day,
The Easter, falls in calendarNot excepting dumb beasts, earthly sufferers everywhere will be united in the next canto "Via Crucis" as "cross-bearers all."
https://www.best-poems.net/herman-melville/via-crucis.html
Getting back to the Russian, he seems to have been conjured by Clarel's musing at David's well--most directly and significantly, perhaps, on the theme of striving against materialists with knife-like personalities.
I don't know why Melville made this particular worldling a Russian. Or why this good-looking Russian comes down out of the grape vines, bent on identifying our Prince-like Lyonese "prodigal" as a Jew. Did Melville have in mind any real life model? Maybe his pre-determined agenda, disclosed in the Russian's interrogation of Clarel, in some way comments on or reflects anti-Semitism associated with Russia. Deplored in the next decade as "Russian Judeophobia":
John Gretchko asks a different question, framed to highlight the importance of winding up the narrative at Easter as observed in the Greek Orthodox Church. John, if agreeable I hope you will say more about the significance of the Prodigal, the Russian, and Orthodox Easter in Melville's Clarel.