Only God can cleanse your heart from its impurities. David knew this and prayed, ‘Create in me a clean heart, O God, and renew a right spirit within me’ (Ps. 51:10). God does that for all who believe on Jesus Christ. He does it judicially in the moment of our belief. He does it practically during the moments of our earthly life as we yield to the gentle urging of His Holy Spirit. He will do it finally and completely in the moment of our death as we are then purified from all evil and brought without spot into His holy presence. – James Montgomery Boice, The Sermon on the Mount