The thoughts of the wicked (or, evil devices) are an abomination to the Lord. Although the Decalogue, by forbidding coveting, showed that God's Law touched the thought of the heart as well as the outward action, the idea here refers to wicked plans or designs, rather than emphatically to the secret movements of the mind.
These have been noticed in Proverbs 15:11. But the words of the pure are pleasant words; literally, pure are words of pleasantness; i.e. words of soothing, comforting tone are, not an abomination to the Lord, as are the devices of the wicked, but they are pure in a ceremonial sense, as it were, a pure and acceptable offering.
Revised Version, pleasant words are pure. Vulgate, "Speech pure and pleasant is approved by him"—which is a pharaphrase of the clause. Septuagint, "The words of the pure are honoured ( σεμναί)."