Proverbs 24:9 - Matthew Poole's English Annotations on the Holy Bible

The thought of foolishness is sin; the very inward thought or contrivance of evil, of which he spake Proverbs 24:8, even before it break forth into action, it is a sin in God's sight, and it is hateful to God. Or foolishness is put for foolish or wicked men, by comparing this with the next clause where the scorner is opposed to it. So the sense is, All the thoughts of wicked men are only evil, and that continually, as is said of man in his corrupt estate, Genesis 6:5, and therefore abominable to God. The scorner; he who not only deviseth and practiseth wickedness, but obstinately persists in it, and rejects all admonitions against it. Is an abomination to men; is abominable not only to God, as all sinners are, but to all sober men.