What is the nature of “sound doctrine,” a phrase Paul uses five times (1 Tim. 1:10; 2 Tim. 1:13; 4:3; Titus 1:9; 2:1)? That doctrine is “sound” (Gk. hygiainō, lit., “hygienic”) suggests that its teaching is more than technically true. On several occasions Paul introduces his teaching with a variation on the following formula: “the saying is sure [i.e., trustworthy] and worthy of full acceptance” (1 Tim. 1:15; 3:1; 4:9; 2 Tim. 2:11; Titus 3:8). These trustworthy sayings are more than propositional statements to be gathered into a system of truths, more than a collection of authoritative statements by Chairman Paul. They are rather statements of understanding that indicate a grasp of the meaning and significance of what God has done in Christ. Accordingly, they are statements that call for personal (and practical) appropriation, not mere theoretical acknowledgment. They are statements that call for their hearers to exercise trust and to respond not only with one’s mind but also with one’s whole being: heart, soul, and strength. Doctrine explicitly tells us what is and how things are; it also implicitly asks us to trust that this is how things are to the point of staking one’s life on it.
– Kevin Vanhoozer in Faith Speaking Understanding: Performing the Drama of Doctrine