I hate vain thoughts - This commences a new portion of the psalm, distinguished by the Hebrew letter Samech (ס s), answering to our “s.” The word rendered “vain thoughts” occurs only in this place. It is rendered by the Septuagint, παρανόμους paranomous - transgressors. So the Latin Vulgate. Luther renders it “die Flattergeister,” the frivolous-minded. The word means divided; a man of a divided mind; a man who has no sure faith in regard to divine things, but is driven here and there; a sceptic; a doubter. Compare James 1:8. Thus it refers not to his own thoughts primarily, as being “vain” or worthless, but to a state of mind or heart in general, where there is no firmness, no stability, no settled view: a state of mind wavering, doubtful, skeptical, in regard to religion. What is implied here in reference to what he loved - by stating (in the way of contrast) what he “hated,” - would be a mind which was settled in its convictions of truth, and firm in its adherence to truth; a mind which was steadfast in religion, and not vacillating, skeptical, or uncertain on the subject. This denotes that the psalmist sought such a state of mind for himself, and that he valued it in others.
But thy law do I love - I have no “divided” or unsettled feelings in regard to that. I am conscious of a firm attachment to it. This thought he has repeatedly expressed in the psalm.