Psalms 66:18

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 Psalms 18:41; Psalms 34:15; Proverbs 1:28; Proverbs 15:29; Proverbs 28:9; Isaiah 15:1-9; Jeremiah 11:11; Jeremiah 14:12; Zechariah 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.