He meditates iniquity upon his bed Here the sacred writer shows that the wickedness of the ungodly man is of a secret and very determined character. It sometimes happens that many, who otherwise are not disposed to wickedness, err and fall into sin, because occasion presents itself all on a sudden; but David tells us, that the wicked, even when they are withdrawn from the sight of men, and in retirement, form schemes of mischief; and thus, although there is not presented before them any temptation, or the evil example of others to excite them to it, they, of their own accord, devise mischief, and urge themselves to it without being impelled by any thing else. Since he describes the reprobate by this distinguishing mark of character, that they devise mischief upon their beds, true believers should learn from this to exercise themselves when alone in meditations of a different nature, and to make their own life the subject of examination, so that they may exclude all evil thoughts from their minds. The Psalmist next refers to their stubbornness, declaring that they set themselves in a crooked and perverse way; that is to say, they purposely and wilfully harden themselves in doing evil. Finally, he adds the reason of their doing this: They abhor not evil Wilfully shutting their eyes, they rush forward in their headlong course till they spontaneously yield themselves the slaves of wickedness. Let us now shortly state the contrast between the ungodly and the people of God, contained in the preceding verses. The former deceive themselves by flattery; the latter exercise over themselves a strict control, and examine themselves with a rigid scrutiny: the former, throwing loose the reins, rush headlong into evil; the latter are restrained by the fear of God: the former cloak or disguise their offenses by sophistry, and turn light into darkness; the latter willingly acknowledge their guilt, and by a candid confession are brought to repentance: the former reject all sound judgment; the latter always desire to vindicate themselves by coming to the open light of day: the former upon their bed invent various ways of doing evil; the latter are sedulously on their guard that they may not devise or stir up within themselves any sinful desire: the former indulge a deep and fixed contempt of God; the latter willingly cherish a constant displeasure at their sins.

He deviseth mischief upon his bed - Margin, as in Hebrew: "vanity." That is, when he lies down; when he is wakeful at night; he plots some scheme of iniquity - some vain, wicked enterprise. So in Proverbs 4:16, "For they sleep not, except they have done mischief; and their sleep is taken away, unless they cause some to fall."
He setteth himself - That is, he takes his stand or his position; he assumes this attitude. See Psalm 2:2, "The kings of the earth "set themselves,"" where the same word occurs. The meaning is that what is done by him is the result of a calm and deliberate purpose. It is not the effect of passion or temporary excitement, but it is a deliberate act in which the mind is made up to do the thing. The conduct here referred to is thus distinguished from rash and hasty acts, showing that this is the settled character of the man.
In a way that is not good - In a bad or wicked way; in a way in which no good can be found; in conduct which allows of no redeeming or mitigating circumstances, and for which there can be no apology.
He abhorreth not evil - He has no aversion to evil. He is not in any manner deterred from doing anything because it is wrong. The fact that it is sinful is not allowed to be a consideration affecting his mind in determining what he shall do. In other words, the moral quality of an action does not influence him at all in making up his mind as to how he shall act. If it is right, it is by accident, and not because he prefers the right; if it is wrong, that fact does not in any way hinder him from carrying his purpose into execution. This is, of course, the very essence of depravity.

He deviseth mischief upon his bed - He seeks the silent and undisturbed watches of the night, in order to fix his plans of wickedness.
He setteth himself - Having laid his plans he fixes his purpose to do what is bad; and he does it without any checks of conscience or abhorrence of evil. He is bent only on mischief, and lost to all sense of God and goodness. A finished character of a perfect sinner.

He (d) deviseth mischief upon his bed; he setteth himself in a way [that is] not good; he abhorreth not evil.
(d) By describing at large the nature of the reprobate, he admonishes the godly to beware of these vices.

He deviseth mischief upon his bed,.... He casts about in his mind on his pillow, when at leisure from all employment; and consults and contrives schemes how to compass his lusts, and to do injury to others, without doing which he cannot sleep;
he setteth himself in a way that is not good, in an evil way, which he chooses and delights in, and determines to continue in, he leaving the paths of righteousness to walk in the ways of darkness:
he abhorreth not evil; which is to be abhorred both because of its nature and effects; see Romans 12:9; but on the contrary he loves it, takes pleasure in doing it, and in them that commit it: thus, by his thoughts, words, and actions, he appears to be devoid of the fear of God.

Deviseth - Freely, from his own inclination, when none are present to provoke him to it.