This is a trustworthy saying: This phrase appears only in the letters to Timothy and Titus (1 Timothy 3:1; 4:8–9; 2 Timothy 2:11–13; Titus 3:4–8). These sayings are probably quotes from tradition that Paul has adapted for the current situation. The saying emphasizes the mercy shown to Paul, but it also offers correction to the false teachers. The saying emphasizes Christ's arrival in history to save sinners.
This saying was probably being suppressed in some way by the false teachers, who focused on:
law (1 Timothy 1:7),
special knowledge (6:20; see also Titus 1:16), and
rules like those in 1 Timothy 4:3 (see also Colossians 2:16–23).