When Doctrine is Unsavory

... and being fervent in spirit, he was speaking and teaching accurately the things concerning Jesus... (Acts 18:25)

When is the doctrine of God's Word unsavory? When it is taught absent personal zeal.

Doctrine without zeal is either like a sword in the hand of a madman, or else it lieth still as cold and without use, or else it serveth for vain and wicked boasting. For we see that some learned men become slothful; other some (which is worse) become ambitious; other some (which is of all the worst) trouble the Church with contention and brawling. Therefore, that doctrine shall be unsavory which is not joined with zeal.

- John Calvin, Commentary on Acts, 2:154.

An armed lunatic. An impotent craftsman. A wicked braggart. A slothful steward. An ambitious cleric. A contentious churchman.

Do not despise the zealous preacher... there are many options that are much worse.