Charles H. Spurgeon on Psalms 66:18

If I regard iniquity in my heart, the Lord will not hear me.

1. They regard iniquity in their heart, who practise it secretly, who are under restraint from the world, but are not possessed of an habitual fear of the omniscient God, the searcher of all hearts, and from whose eyes there is no covering of thick darkness where the workers of iniquity may hide themselves. Jer 23:24.

2. They regard iniquity in the heart, who entertain and indulge the desire of sin, although in the course of providence they may be restrained from the actual commission of it. I am persuaded the instances are not rare, of men feeding upon sinful desires, even when through want of opportunity, through the fear of man, or through some partial restraint of conscience, they dare not carry them into execution.

3. They regard iniquity in their heart, who reflect upon past sins with delight, or without sincere humiliation of mind. Perhaps our real disposition, both towards sin and duty, may be as certainly discovered by the state of our minds after, as in the time of action. The strength and suddenness of temptation may betray even a good man into the commission of sin; the backwardness of heart and power of inward corruption may make duty burdensome and occasion many defects in the performance; but every real Christian remembers his past sins with unfeigned contrition of spirit, and a deep sense of unworthiness before God; and the discharge of his duty, however difficult it may have been at the time, affords him the utmost pleasure on reflection. It is otherwise with many; they can remember their sins without sorrow, they can speak of them without shame, and sometimes even with a mixture of boasting and vain glory. Did you never hear them recall their past follies, and speak of them with such relish, that it seems to be more to renew the pleasure than to regret the sin? Even supposing such persons to have forsaken the practice of some sin, if they can thus look upon them with inward complacency, their seeming reformation must be owing to a very different cause from renovation of heart.

4. They regard iniquity in their heart, who look upon the sins of others with approbation; or, indeed, who can behold them without grief. Sin is so abominable a thing, so dishonouring to God, and so destructive to the souls of men, that no real Christian can witness it without concern. Hence it is so frequently taken notice of in Scripture, as the character of a servant of God, that he mourns for the sins of others. Ps 119:136,158.

5. In the last place, I suspect that they regard sin in the heart, who are backward to bring themselves to the trial, and who are not truly willing that God himself would search and try them. If any, therefore, are unwilling to be tried, if they are backward to self examination, it is an evidence of a strong and powerful attachment to sin. It can proceed from nothing but from a secret dread of some disagreeable discovery, or the detection of some lust which they cannot consent to forsake... There are but too many who though they live in the practice of sin, and regard iniquity in their hearts, do yet continue their outward attendance on the ordinances of divine institution, and at stated times lay hold of the seals of God's covenant. Shall they find any acceptance with him? No. He counts it a profane mockery; he counts it a sacrilegious usurpation. Ps 50:16-17. Shall they have any comfort in it? No: unless in so far as in righteous judgment he suffers them to be deceived; and they are deceived, and they are most unhappy, who lie longest under the delusion. Ps 50:21. Shall they have any benefit by it? No: instead of appeasing his wrath, it provokes his vengeance; instead of enlightening their minds, it blinds their eyes; instead of sanctifying their nature, it hardens their hearts. See a description of those who had been long favoured with outward privileges and gloried in them. Joh 12:39-40. So that nothing is more essential to an acceptable approach to God in the duties of his worship in general, and particularly to receiving the seals of his covenant, than a thorough and universal separation from all known sin. Job 11:13-14. John Witherspoon (1722-1749), in a Sermon entitled "The Petitions of the Insincere Unavailing."

Verses 18-20. Lord, I find David making a syllogism, in mood and figure, two propositions he perfected. If I regard iniquity in my heart, the Lord will not hear me; but verily God hath heard me; he hath attended to the voice of my prayer. Now I expected that David should have concluded thus: "Therefore I regard not wickedness in my heart; but far otherwise he concludes": Blessed be God, which hath not turned away my prayer, nor his mercy from me. Thus David had deceived, but not wronged me. I looked that he should have clapped the crown on his own, and he puts it on God's head. I will learn this excellent logic; for I like David's better than Aristotle's syllogisms, that whatsoever the premise be, I make God's glory the conclusion. Thomas Fuller.