“For I know this, that after my departing shall grievous wolves enter in among you, not sparing the flock.  Also of your own selves shall men arise, speaking perverse things, to draw away disciples after them.”  Acts 20:29-30  (KJB)

Paul, by the revelation of the Spirit of God, knew that when he was departed seducers, voracious, and evil men would come in and try to destroy the word and work of God. There are two types of voracious leadership named here.  I will let some sages from the past clarify who they are…

From John Gills Exposition of the Bible…

For I know this,…. By divine revelation:
that after my departing; either out of this world, or after his leaving them now, and proceeding on, his journey:
shall grievous wolves enter in among you; false teachers, comparable to wolves, for their craft and cunning, and for their greedy, covetous, and voracious dispositions; and who would be very grievous, troublesome, and even intolerable to them; these, he knew, would enter privily, at an unawares, into their churches, and set up themselves for preachers, without being called or sent:
not sparing the flock; fleecing it instead of feeding it, making merchandise of it, and like the Pharisees, under religious pretences, devour widows’ houses, and drain the purses of men; and having as little compassion upon their souls, poisoning them with their errors and heresies, subverting their faith, and bringing them into swift ruin and destruction, as much as would in them lie.

From Jamieson, Fausset, and Brown Commentary…

after my departing shall grievous wolves enter in among you — Two classes of coming enemies are here announced, the one more external to themselves, the other bred in the bosom of their own community; both were to be teachers, but the one, “grievous wolves,” not sparing, that is, making a prey of the flock; the other (Act_20:30), simply sectarian “perverters” of the truth, with the view of drawing a party after them. Perhaps the one pointed to that subtle poison of Oriental Gnosticism which we know to have very early infected the Asiatic churches; the other to such Judaizing tendencies as we know to have troubled nearly all the early churches. See the Epistles to the Ephesians, Colossians, and Timothy, also those to the seven churches of Asia (Revelation 2:1-3:22). But watchfulness against all that tends to injure and corrupt the Church is the duty of its pastors in every age.

O my friend draw near to Jesus Christ the Son of the Living God, God the Living Son.