Albert Barnes on Titus 2:8

Sound speech. 1Timm 1:10. He was to use language that would be spiritually healthful (υγιη;) that is, true, pure, uncorrupted.--This word, and its correlatives, is used in this sense, in the New Testament, only by the apostle Paul. It is commonly applied to the body, meaning that which is healthful, or whole. See Lk 5:31, 6:10, 7:10, 15:27, Mt 12:13, 15:31, Mk 3:5, 5:34 Jn 5:4,6,9,11,14,15, 7:23, Acts 4:10, 3Jn 1:2. For Paul's use of the word, see 1Timm 1:10, 6:3, 2Ti 1:13, 4:3, Tit 1:9,13, 2:1,2,8. It does not elsewhere occur.

That cannot be condemned. Such as cannot be shown to be weak, or unsound; such that no one could find fault with it, or such as an adversary could not take hold of and blame. This direction would imply purity and seriousness of language, solidity of argument, and truth in the doctrines which he maintained.

That he that is of the contrary part may be ashamed, etc, Ashamed that he has opposed such views.

(b) "Sound speech" 1Timm 6:3