A man hath joy by the answer of his mouth: and a word spoken in due season, how good is it!
A man hath joy by the answer of his mouth - by every wise and seasonable speech that he utters in conversation, as the parallel clause requires.
And a word (spoken) in due season, how good (is it)! It is as pre-eminently "good" as it is rare (Proverbs 25:11).