Purgatorio XVI, Marco the Lombard tells Dante what is necessary for a wise and just Ruler

'Therefore, one needed law to serve as curb;
a ruler, too, was needed, one who could
discern at least the tower of the true city.

The laws exist, but who applies them now?
No one-the shepherd who precedes his flock
can chew the cud but does not have cleft hooves;

and thus the people, who can see their guide
snatch only at that good for which they feel
some greed, would feed on that and seek no further

Misrule, you see, has caused the world to be
malevolent; the cause is clearly not
celestial forces-they do not corrupt.
For Rome, which made the world good, used to have
two suns; and they made visible two paths-
the world's path and the pathway that is God's.

Each has eclipsed the other; now the sword
has joined the shepherd's crook; the two together
must of necessity result in evil,

because, so joined, one need not fear the other:
and if you doubt me, watch the fruit and flower,
for every plant is known by what it seeds.

Within the territory watered by
the Adige and Po, one used to find
valor and courtesy-that is, before

Frederick was met by strife; now anyone
ashamed of talking with the righteous or
of meeting them can journey there, secure.

True, three old men are there, in whom old times
reprove the new; and they find God is slow
in summoning them to a better life:

Currado da Palazzo, good Gherardo,
and Guido da Castel, whom it is better
to call, as do the French, the candid Lombard.

You can conclude: the Church of Rome confounds
two powers in itself; into the filth,
it falls and fouls itself and its new burden."
"Good Marco," I replied, "you reason well;
and now I understand why Levi's sons were
not allowed to share in legacies.

Purgatorio XVI

In Purgatorio XVI, Marco the Lombard tells Dante what is necessary for a wise and just Ruler: "The Shepherd who is leading you can chew the cud, but lacks the cloven hoof." St Thomas writes on chewing the cud & the cloven hoof as follows: "The animal that chews the cud and has a divided hoof, is clean in signification. Because division of the hoof is a figure of the two Testaments: or of the Father and Son: or of the two natures in Christ: of the distinction of good and evil. While chewing the cud signifies meditation on the Scriptures and a sound understanding thereof; and whoever lacks either of these is spiritually unclean." Many believe that this line: chewing the cud refers to the Pope. I would contend that this line applies to the qualities needed for a wise and just ruler. Correct discernment and understanding of Scripture in defending the rights of the Office of the Emperor (chewing the cud) and the proper and valid election to that office (cloven hoof). Reason for this interpretation of viewing the authority of the Holy Roman Emperor as chewing the cud and cloven hoof follows from studying the contest between the temporal rights of the emperor versus the pope. The popes never had proper understanding of Scripture when defending the papal abuses against the right of the emperor. The popes were simply not able to scripturally defend their papal rights over the rights of the emperor. The popes lacked proper scriptural discernment.

In Dante’s Monarchia (bk III) the Divine Poet destroys all of the papal Scriptural arguments made by the opponents to the Roman Emperor. So in no way would the Divine Poet apply this line to the papacy: 'the Shepherd who is leading you can chew the cud' No, this line does not apply to the Office of the Pope. Because the pope is unable and unwilling to chew the cud in Scriptural matters pertaining to the rights of the Empire. The pope does not have proper scriptual discernment on matters of rights of the Emperor.

Now for the cloven hoof, St Thomas tells us that the cloven hoof is a figure of the two natures in Christ, or His Kingship and His priesthood. There is found in Purgatory XXXII a two natured beast, the Griffin , who's duty or vocation is to pull the Chariot to the tree, which then renews. For many this two natured beast is described as Christ. I would disagree and note that it is reasonable to say that the two natured beast describes the Royal and Sacerdotal natures that make up the Office of the Imperial Electors. Three Sacerdotal and four Royal. St Thomas tells us that: 'in the griffon which is hostile to horses and men, cruelty of powerful men is prohibited.' The griffin or Imperial Electors have a civic duty to fulfill in electing the Roman Emperor. Thus making sure that a Universal ruler can limit the cruelty of powerful men over the rest.

Now back to 'The Shepherd who is leading you can chew the cud, but lacks the cloven hoof.' Even if a Roman ruler possesses right understanding of scripture in defending the rights of the Office of the Emperor but is not properly and validly elected by the Imperial Electors he will fail to be a wise and just Ruler and would be no better than a usurper who would be unable to limit the cruelty of powerful men over the rest.