John Calvin Commentary Titus 2:8

"sound speech, that cannot be condemned; that he that is of the contrary part may be ashamed, having no evil thing to say of us." — Titus 2:8 (ASV)

Sound speech, unblamable: “Sound speech” relates (in my opinion) to ordinary life and familiar conversation, for it would be absurd to interpret it as relating to public instruction, since he only wishes that Titus, both in his actions and in his words, should lead a life that agrees with his preaching. He therefore instructs that his words should be pure and free from all corruption.

Unblamable may apply either to the words or to the person of Titus. I prefer the latter view, that the other nouns in the accusative case (which the Greek syntax easily allows) may depend on it in this sense: “that you may show yourself unblamable in gravity, in integrity, and in sound words.”

That the adversary may be ashamed. Although a Christian man ought to look at other objects, yet this must not be neglected: to shut the mouth of wicked men, as we are everywhere taught that we should give no occasion for slander. Everything that they can seize on as improper in our conduct is maliciously turned against Christ and his doctrine. The consequence is that, through our fault, the sacred name of God is exposed to insult. Accordingly, the more we perceive that we are keenly observed by enemies, let us be the more attentive to guard against their slanders, and thus let their malice strengthen in us the desire of doing well.