Sound (or healthy) doctrine is a major theme in the book of Titus. As Paul wrote, "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" (Titus 1:9).
Sound doctrine is intended to produce people who are sound in the Christian faith. "This testimony is true. Therefore rebuke them sharply, that they may be sound in the faith" (Titus 1:13).
A people of sound faith are able to live sound lives. Most of Titus 2 applies the principles of sound doctrine to the daily responsibilities of believers. Healthy doctrine produces a people with healthy faith who live out that faith in healthy ways.
Then, the apostle Paul presents the foundation of sound doctrine: the grace of God and our need for it. "For the grace of God has appeared, bringing salvation for all people, training us to renounce ungodliness and worldly passions, and to live self-controlled, upright, and godly lives in the present age, waiting for our blessed hope, the appearing of the glory of our great God and Savior Jesus Christ, who gave himself for us to redeem us from all lawlessness and to purify for himself a people for his own possession who are zealous for good works" (Titus 2:11-17).
In order to make progress in the Christian life, we need to remember where we came from. "For we ourselves were once foolish, disobedient, led astray, slaves to various passions and pleasures, passing our days in malice and envy, hated by others and hating one another" (Titus 3:3).
We also need to remember what the Lord has done for us. "But when the goodness and loving kindness of God our Savior appeared, he saved us, not because of works done by us in righteousness, but according to his own mercy, by the washing of regeneration and renewal of the Holy Spirit, whom he poured out on us richly through Jesus Christ our Savior, so that being justified by his grace we might become heirs according to the hope of eternal life" (Titus 3:4-7).
This kind of sound doctrine will keep followers of Christ sound in the faith and productive in the world.