The words of his mouth are iniquity and deceit - Are false and wicked. See the notes at Psalm 12:2. It is words do not fairly represent or express what is in his heart.

He hath left off to be wise - To act wisely; to do right.

And to do good - To act benevolently and kindly. This would seem to imply that there had been a change in his conduct, or that he was not what he once professed to be, and appeared to be. This language would be applicable to the change in the conduct of Saul toward David after he became envious and jealous of him 1 Samuel 18; and it is possible, as Amyraldus supposed, that this may have had particular reference to him. But such instances of a change, of feeling and conduct are not very uncommon in the world, and it may doubtless have happened that David experienced this more than once in his life.

The words of his mouth are iniquity - In the principle; and deceit calculated to pervert others, and lead them astray.

He hath left off to be wise, and to do good - His heart is become foolish, and his actions wicked. He has cut off the connection between himself and all righteousness.

The words of his mouth are iniquity and deceit,.... Not only sinful, but sin itself; his mouth is full of cursing and bitterness, of filthy and unchaste words, of corrupt communication, lying, deceit, and flattery; out of the abundance of the wickedness of his heart his mouth speaketh; and which shows the badness of it, and proves all that is said before of him;

he hath left off to be wise, and to do good; by which the psalmist seems to intend one that had been a professor of religion, who, besides the light of nature he had acted contrary to, had had the advantage of a divine revelation, and had been enlightened into the knowledge of divine things, and had done many things externally good, particularly acts of beneficence; but now had dropped his profession of religion, denied the truths he had been enlightened into, and ceased from doing good; otherwise a natural man understandeth not; and, though he is wise to do evil, to do good he has no knowledge.

The words of his mouth are iniquity and {c} deceit: he hath left off to be wise, and to do good.

(c) The reprobates mock wholesome doctrine, and put no difference between good and evil.

36:3 Left off - Once he had some degrees of wisdom, but now he is become an open apostate.

36:1-4 From this psalm our hearts should be duly affected with hatred of sin, and seek satisfaction in God's loving-kindness. Here is the root of bitterness, from which all the wickedness of wicked men comes. It takes rise from contempt of God, and the want of due regard to him. Also from the deceit they put upon their own souls. Let us daily beg of God to preserve us from self-flattery. Sin is very hurtful to the sinner himself, and therefore ought to be hateful; but it is not so. It is no marvel, if those that deceive themselves, seek to deceive all mankind; to whom will they be true, who are false to their own souls? It is bad to do mischief, but worse to devise it, to do it with plot and management. If we willingly banish holy meditations in our solitary hours, Satan will soon occupy our minds with sinful imaginations. Hardened sinners stand to what they have done, as though they could justify it before God himself.