Since an Overseer is Entrusted with God's Work (Titus 1:7-9)

Since an overseer is entrusted with God's work, he must be blameless--not overbearing, not quick-tempered, not given to drunkenness, not violent, not pursuing dishonest gain. Rather he must be hospitable, one who loves what is good, one who is self-controlled, upright, holy, and disciplined. He must hold firmly to the trustworthy message as it has been taught so that he can encourage others by sound doctrine and refute those who oppose it.

What does Scripture say about the importance of knowing sound doctrine, i.e., not enough to do good works, and the connection of our character to our testimony?