What does Psalm 66:18 mean?

God is never obligated to give people their desires, regardless of how pious a person may be. And yet, Scripture also indicates that God is more inclined to hear the prayers of those who honor Him and avoid evil in their own hearts. In part, this is because those who truly honor God are more attuned to His will: what they ask for is more likely to be what He has already planned. God doesn't ignore a believer's prayers, even if they sin. But the prayers of someone with no respect for God aren't likely to be answered.

To "cherish iniquity" is to treat evil as something worth protecting. Rather than rooting it out, confessing, and repenting, a person can hold it dear and refuse to be corrected. Such disregard for God's law makes prayer an abomination to God (Proverbs 28:9). Isaiah 59:2 reveals that sin separates sinners from God. Despite how one tries to cover up evil thoughts and attitudes, God sees the heart.

Proverbs 28:13 offers both a warning and a promise. The warning is, "Whoever conceals his transgressions will not prosper." The promise is, "But he who confesses and forsakes them will obtain mercy." The Holy Spirit convicts of sin (John 16:9) so a sinning believer will confess his sin and receive forgiveness. First John 1:9 promises: "If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness."