Charles H. Spurgeon on Psalms 66:18

If I regard iniquity in my heart, the Lord will not hear me. Though the subject matter of a saint's prayer be founded on the word, yet if the end he aims at be not levelled right, this is a door at which his prayer will be stopped: "Ye ask, and receive not, because ye ask amiss, that ye may consume it upon your lusts." Jas 4:3. Take, I confess, a Christian in his right temper, and he aims at the glory of God; yet, as a needle that is touched with a loadstone may be removed from its point to which nature hath espoused it, though trembling till it again recovers it; so a gracious soul may in a particular act and request vary from this end, being jogged by Satan, yea, disturbed by an enemy nearer home —his own unmortified corruption. Do you not think it possible for a saint, in distress of body and spirit, to pray for health in the one, and comfort in the other, with too selfish a respect to his own ease and quiet? Yes, surely; and to pray for gifts and assistance in some eminent service, with an eye to his own credit and applause; to pray for a child with too inordinate a desire that the honour of his house may be built up in him. And this may be understood as the sense, in part, of that expression, If I regard iniquity in my heart, the Lord will not hear me. For though to desire our own health, peace, and reputation, be not an iniquity, when contained within the limits that God hath set; yet, when they overflow at such a height, as to overtop the glory of God, yea, to stand but in a level with it, they are a great abomination. That which in the first or second degree is wholesome food, would be rank poison in the fourth or fifth: therefore, Christian, catechize thyself, before thou prayest: O, my soul, what sends thee on this errand? Know but thy own mind what thou prayest for, and thou mayest soon know God's mind how thou shalt speed. Secure God his glory, and thou mayest soon know God's mind how thou shalt speed. William Gurnall.