Jehovah knoweth the thoughts of men, etc. He again insists upon the folly of men in seeking to wrap themselves up in darkness, and hide themselves from the view of God. To prevent them from flattering themselves with vain pretexts, he reminds them that the mists of delusion will be scattered at once when they come to stand in God's presence. Nothing can avail them, so long as God from heaven stamps vanity upon their deepest counsels. The Psalmist's design in citing them before the Judge of all, is to make them thoroughly search and try their own hearts; for the great cause of their self-security lay in failing to realize God, burying all distinction between right and wrong, and, so far as that was possible, hardening themselves against all feeling. They might contrive to soothe their minds by means like these, but he tells them that God ridiculed all such trifling. The truth may be a plain one, and well known; but the Psalmist states a fact which many overlook, and which we would do well to remember, That the wicked, when they attempt to hide themselves under subtile refuges, cannot deceive God, and necessarily deceive themselves. Some read -- They (that is, men themselves) are vanity; but this is a forced rendering, and the form of expression is one which both in the Greek and Hebrew may be translated, God knows that the thoughts of men are vain.

The Lord knoweth the thoughts of man - That is, He who teaches people all that they know Psalm 94:10, must understand all that there is in the mind. See the notes at 1-Corinthians 3:20.
That they are vanity - That is, that they are foolish, vain, unwise, wicked. The knowledge of the thoughts themselves carries with it also the knowledge that they are vain and foolish - for that is their character, and to know them truly is to know this of them. They do not appear to him as they do to people themselves. They are to his view stripped of all that is flattering and illusive, and are seen to be vain and foolish.

The Lord knoweth the thoughts of man,.... He not only hears their words, and sees their actions; but he knows their thoughts, the secret thoughts of their hearts, though he is afar off from them, and, they from him; he is the searcher of the hearts and trier of the reins of the children of men; see Psalm 139:2, and so is Christ, who is the omniscient God, and is the Jehovah all along spoken to and of in this psalm; he knows the thoughts of men, and is a critical discerner of them, Matthew 9:3.
that they are vanity; either that their thoughts are vanity; the object of them is vanity, the riches and honours of this world, which are all vanity and vexation of spirit; and sinful lusts and pleasures, which are vain and useless, yea, pernicious and hurtful: and so they are in their issue and event; they come to nothing, they are without effect; the Lord disappoints men's devices, and frustrates their designs; they think of this and the other, form schemes, but cannot execute them: or else the sense is, that they themselves are vanity, as man in his best estate is; even every man, whether of high or low degree; see Psalm 39:5. The Syriac version is, "for they are a vapour"; with which compare James 4:14. Thales, an Heathen philosopher (e), being asked whether men's deeds could be hid from God, answered, no, nor their thoughts.
(e) Apud Laert. Vit. ejus, Valer. Maxim. l. 7. c. 2. extern. 8.

Thoughts - Yes, he knoweth all things, even the most secret things, as the thoughts of men; and in particular your thoughts; much more your practices.