Psalms 66:18

We should declare unto those that fear God, what he has done for our souls, and how he has heard and answered our prayers, inviting them to join us in prayer and praise; this will turn to our mutual comfort, and to the glory of God. We cannot share these spiritual privileges, if we retain the love of sin in our hearts, though we refrain from the gross practice, Sin, regarded in the heart, will spoil the comfort and success of prayer; for the sacrifice of the wicked is an abomination of the Lord. But if the feeling of sin in the heart causes desires to be rid of it; if it be the presence of one urging a demand we know we must not, cannot comply with, this is an argument of sincerity. And when we pray in simplicity and godly sincerity, our prayers will be answered. This will excite gratitude to Him who hath not turned away our prayer nor his mercy from us. It was not prayer that fetched the deliverance, but his mercy that sent it. That is the foundation of our hopes, the fountain of our comforts; and ought to be the matter of our praises.

If I regard iniquity in my heart. If, having seen it to be there, I continue to gaze upon it without aversion; if I cherish it, have a side glance of love toward it, excuse it, and palliate it; The Lord will not hear me. How can he? Can I desire him to connive at my sin, and accept me while I wilfully cling to any evil way? Nothing hinders prayer like iniquity harboured in the breast; as with Cain, so with us, sin lieth at the door, and blocks the passage. If thou listen to the devil, God will not listen to thee. If you refuse to hear God's commands, he will surely refuse to hear thy prayers. An imperfect petition God will hear for Christ's sake, but not one which is wilfully miswritten by a traitor's hand. For God to accept our devotions, while we are delighting in sin, would be to make himself the God of hypocrites, which is a fitter name for Satan than for the Holy One of Israel.