'Sound' in the Bible

holding to the faithful message as taught, so that he will be able both to encourage with sound teaching and to refute those who contradict it.

This testimony is true. So, rebuke them sharply, that they may be sound in the faith

But you must say the things that are consistent with sound teaching.

Older men are to be level headed, worthy of respect, sensible, and sound in faith, love, and endurance.

Your message is to be sound beyond reproach, so that the opponent will be ashamed, having nothing bad to say about us.