Keep... with all diligence. Above all that must be guarded. The preposition. (hebrew character) marks the place or person that keeps: the meaning being, guard the heart as the great citadel, for out of it are the source and outgoings of life. Same word as in verses: Proverbs 6:13. Not the same word as in verses: Proverbs 4:21.
froward. See notes on Proverbs 2:12 and Proverbs 6:12, the only other examples of frowardness of mouth.
(23-27) Note the Alternation in these verses. Positive. Heart. Negative. Mouth. Positive. Eyes. 27. Negative. Feet.