Adam Clarke on Titus 2:1

But speak thou the things - This is a conclusion drawn from the preceding chapter: the Judaizing teachers not only taught a false doctrine, but they led an unholy life; Titus was to act directly opposite; he must teach a sacred doctrine, and the things which become it; he must proclaim the truth, and illustrate that truth. The people must not only be well instructed, but they must be holy in their lives. Principle and practice must go hand in hand.