Jamieson, Fausset and Brown on Titus 2:1

CHAPTER 2

Tit 2:1-15. Directions to Titus: How to Exhort Various Classes of Believers: The Grace of God in Christ Our Grand Incentive to Live Godly.

1. But ... thou--in contrast to the reprobate seducers stigmatized in Tit 1:11, 15, 16. "He deals more in exhortations, because those intent on useless questions needed chiefly to be recalled to the study of a holy, moral life; for nothing so effectually allays men's wandering curiosity, as the being brought to recognize those duties in which they ought to exercise themselves" [Calvin].

speak--without restraint: contrast Tit 1:11, "mouths ... stopped."

doctrine--"instruction" or "teaching."