He must hold firm to the trustworthy word as taught, so that he may be able to give instruction in sound doctrine and also to rebuke those who contradict it.
As a pastor and as an elder, I must be a man of the Word. I have to know scripture, understand scripture, all so that I can skillfully shepherd by teaching scripture. From the Word of God comes solid, wise instruction that Paul calls "sound doctrine". Paul means to tell us that this is the source of the church's spiritual health.
Leaders should be evaluated not on their social skills alone (after all, false teachers are quite winsome), neither on their administrative prowess alone (legalism can get things done), nor on their speaking ability alone (the devel can alluringly captivate listeners with a dressed up lie from hell). Leaders must possess, at their core, gospel-infused character and a passion for baseline strong biblical doctrine. That is the kind of leadership health that will make healthy disciples and build strong local churches. Doctrine must be preached, believed, defended, and perpetuated.
I'm concerned that current cultural evangelical Christianity is alarmingly weak on what Paul made absolutely essential. There is no other explanation for "Your Best Life Now". We are decaying rapidly from the head down. God... raise up Christian leaders once again who are gospel-centered, holy men, men who are Bible-saturated and passionate in sound doctrine!