Murder all his hearers at once!

(Thomas Brooks, "The Crown and Glory of Christianity,
 or, HOLINESS, the Only Way to Happiness", 1662)

"The leaders of the people have led them down the
 path of destruction." Isaiah 9:16

Take heed of settling yourselves under an unholy minister
—of one whose life gives the lie to his doctrine. An unholy
preacher is the greatest destroyer of the souls of men! He
who preaches well—but lives bad—does what he can, to
murder all his hearers at once! There is no greater
bar to holiness, than ministers' unholy lives. An unholy
life mars the soundest and the sweetest doctrine. The
sins of teachers
are the teachers of sins!

An unholy minister is the greatest pest, the worst
plague
, and the greatest mischief—that can be to
a people; for his enormities, his wickednesses, will
have the strongest influences upon the souls and
lives of men—to make them eternally miserable.
His falls will be the fall and ruin of many; for
people are prone to . . .
  live more by examples—than by precepts;
  mind more what the minister doesthan what he says;
  eye more how he walks—than how he talks.

Let a minister be ever so learned, solid, quaint, elegant,
zealous, judicious, sententious, etc.—yet if he is carnal,
covetous, worldly, vain, and loose in his life and walk,
his hearers will rather slight and abhor the holy things
of God.

When the preacher departs out of the way of holiness,
the people will quickly wander from all that is good. He
whose life is not a standing reproof to sin, will, by his
life, encourage sinners more and more in a way of sin.
There is nothing which keeps men so off from the love
of holiness, and from the pursuing after holiness—than
the unholy lives of their ministers.

"Watch your life and doctrine closely." 1 Timothy 4:16

"Set an example for the believers in speech, in life,
 in love, in faith and in purity." 1 Timothy 4:12


"In everything set them an example by doing what
 is good." Titus 2:7