If I regard iniquity in my heart - literally, "If I have seen iniquity in my heart." That is, If I have indulged in a purpose of iniquity; if I have had a wicked end in view; if I have not been willing to forsake all sin; if I have cherished a purpose of pollution or wrong. The meaning is not literally, If I have "seen" any iniquity in my heart - for no one can look into his own heart, and not see that it is defiled by sin; but, If I have cherished it in my soul; if I have gloated over past sins; if I am purposing to commit sin again; if I am not willing to abandon all sin, and to be holy.
The Lord will not hear me - That is, He will not regard and answer my prayer. The idea is, that in order that prayer may be heard, there must be a purpose to forsake all forms of sin. This is a great and most important principle in regard to prayer. The same principle is affirmed or implied in Psalm 18:41; Psalm 34:15; Proverbs 1:28; Proverbs 15:29; Proverbs 28:9; Isaiah 15:1-9; Jeremiah 11:11; Jeremiah 14:12; Zac 7:13; John 9:31. It is also especially stated in Isaiah 58:3-7. The principle is applicable
(a) to secret purposes of sin; to sinful desires, corrupt passions. and evil propensities;
(b) to acts of sin in individuals, as when a man is pursuing a business founded on fraud, dishonesty, oppression, and wrong;
(c) to public acts of sin, as when a people fast and pray Isaiah 58:1-14, and yet hold their fellow-men in bondage; or enact and maintain unjust and unrighteous laws; or uphold the acts of wicked rulers; or countenance and support by law that which is contrary to the law of God; and
(d) to the feelings of an awakened and trembling sinner when he is professedly seeking salvation.
If there is still the love of evil in his heart; if he has some cherished purpose of iniquity which he is not willing to abandon; if there is any one sin, however small or unimportant it may seem to be, which he is not willing to forsake, he cannot hope that God will hear his prayer; he may be assured that he will not. All prayer, to be acceptable to God, must be connected with a purpose to forsake all sin.

If I regard iniquity in my heart - "If I have seen (ראיתי raithi) iniquity in my heart," if I have known it was there, and encouraged it; if I pretended to be what I was not; if I loved iniquity, while I professed to pray and be sorry for my sin; the Lord, אדני Adonai, my Prop, Stay, and Supporter, would not have heard, and I should have been left without help or support.

(k) If I regard iniquity in my heart, the Lord will not hear [me]:
(k) If I delight in wickedness, God will not hear me, but if I confess it, he will receive me.

If I regard iniquity in my heart,.... There was iniquity in his heart, as there is in every good man's heart, and a great deal too; it is full of it; and it should be regarded in some sense, so as to guard against it, and pray to be kept from it, that it may not break forth into action; and so as to loath it, abhor it, and be humbled for it; but not so as to nourish and cherish it, to take delight and pleasure in it: or "if I look upon it" (h), as it may be rendered; that is, with approbation of it, and satisfaction in it, and ordered his conversation according to it; or acted the deceitful and hypocritical part in prayer; or had any evil intention in his petitions, to consume on his lusts what he asked for;
the Lord will not hear me; for the Lord hears not sinners that delight in sin, and live in it; neither profane sinners nor hypocrites; see John 9:31.
(h) "si vidi", Pagninus, Montanus; "si aspexi", V. L. "si conspexi", Gejerus.

If I regard iniquity in my heart--literally, "see iniquity with pleasure."

Iniquity - Any sin. In heart - If my heart had been false to God, although I might have forborne outward acts. If I had been guilty of that, by heart was set upon sin, or I desired only that which I resolved in my heart to spend upon my lusts.