One of the biggest responsibilities of the pastor/shepherd, besides feeding the sheep, is to protect the sheep from wolves without and wolves within. This often takes more time and effort since sheep are always willing and able to eat. They're not, however, always very willing to change or move.
As far as protecting from the sheep within, they are always dressed in sheep's clothing, which makes it more challenging to recognize them for one, and convince the real sheep for another thing. But it's for their protection--eternity is at stake. Sometimes the shepherd will say--there is a wolf amongst us. Stopping there would be cruel. He must then describe it, call it out, expose it, and then once all their attention is drawn to that particular wolf in sheep's clothing, begin to show very carefully all the places where the imposter can be seen. "See right there, where the snout sticks out under the fur?" "No, pastor, I still don't see it." "Well, it's supposed to look like this, but instead it looks terribly like this...see it now?" "Oh my!"
Sometimes a wolf in sheep's clothing has been in the flock for so long some of the decieved sheep have grown quite fond of him, though his only purpose is to devour them in the end. This takes much care, pleading, patience, precise exposition of his wolf-ness, etc. Eternity is at stake.
Sometimes the wolf in sheep's clothing has grown so comfortable and sly and cunning that he is almost appointed the shepherd. Woe to the flock without a pastor who will lay a strong foundation.
And, regarding precise teaching, and a 'systematic agenda':
Counterfeit spotters prepare for their work by studying nothing but the original, true. But they do this so rigorously becuase the entire economy would collapse if counterfeiters were not vigorously and continually hunted down and eradicated. They are protectors of the economy as pastors are protectors of the flock.