Ye eat the fat - I think החלב hacheleb should be translated the milk, and so most of the Versions understand it. Or they lived on the fat sheep, and took the wool of all.
"The priests," says Calmet, "ate the tithes, the first-fruits, and the offerings of the people; the princes received the tributes and imposts and instead of instructing and protecting them, the latter took away their lives by the cruelties they practiced against them: the former destroyed their souls by the poison of their doctrine, and by their bad example. The fat sheep point out the rich to whom these pastors often disguised the truth, by a cruel condescension and complaisance."

Ye eat the (b) fat, and ye clothe yourselves with the wool, ye kill them that are fed: [but] ye feed not the flock.
(b) You seek to enrich yourselves by their conveniences and to spoil their riches and substance.

Ye eat the fat,.... The Septuagint, Vulgate Latin, and Arabic versions, render it, "the milk"; the words for fat and milk differ only in the points; and this was not unlawful, for
who feedeth a flock, and eateth not of the milk of the flock? 1-Corinthians 9:7, provided it was done with moderation, that they ate some, but not all; but these rulers milked their subjects too much, oppressed them with heavy taxes, and got their substance into their own hands. The Targum is,
"ye eat the good;''
they got possessed of the best of their substance; as did also their ecclesiastical rulers, who were greedy shepherds, that could never have enough; they looked for their gain from their quarter, and even devoured widows' houses, Isaiah 56:11,
ye clothe you with the wool: the pure wool, as the Targum, the finest of it; they fleeced the flock, and stripped the people of their riches; and minded nothing but their own backs and bellies:
ye kill them that are fed; or, that "are fat" (q); the richest of the people they brought accusations and charges against for capital crimes; and so put them to death under a colour of justice, that they, might get their estates into their hands:
but ye feed not the flock; did not govern the people well, by doing justice and judgment among men, as became civil magistrates; did not deliver out words of faith and sound doctrine, to feed the souls of men with, which is the duty of those that preside in the church of God.
(q) "quod pingue est", Vatablus, Bochartus; "pinguem", Cocceius, Starckius. So Ben Melech.

fat--or, by differently pointing the Hebrew, "milk" [Septuagint]. Thus the repetition "fat" and "fed" is avoided: also the eating of "fat" would not probably be put before the "killing" of the sheep. The eating of sheep's or goats' milk as food (Deuteronomy 32:14; Proverbs 27:27) was unobjectionable, had not these shepherds milked them too often, and that without duly "feeding" them [BOCHART], (Isaiah 56:11). The rulers levied exorbitant tributes.
kill . . . fed--kill the rich by false accusation so as to get possession of their property.
feed not . . . flock--take no care of the people (John 10:12).

Ye kill - You contrive methods, to take first the life, and next the estate of the well - fed, the rich and wealthy. But - You take care to lead, protect, provide for, and watch over them.