How do we understand the phrase 'if I regard iniquity in my heart, the Lord will not hear me'?

This phrase from Psalm 66:18 has often been a source of concern for believers. It signifies that if we cling to our iniquity and attempt to approach God based on our merits or perceived righteousness, our prayers will not be heard. This understanding aligns with the Reformed view that emphasizes reliance on Christ's finished work for salvation and acceptance before God. Our righteousness, as Scripture states, is as 'filthy rags' (Isaiah 64:6). Thus, to approach God, we must come through the blood of Christ, recognizing our need for His grace. Only through this lens can we have confidence that God hears our pleas and has mercy on us.