Why is it dangerous to rely on our own righteousness?

Throughout His ministry, Jesus confronted the Pharisees and religious leaders for their misplaced trust in their own righteousness. In Matthew 23:13–15, He warns them that their actions, which are presumed righteous in their eyes, actually shut the door to heaven for themselves and others. This reliance on human righteousness blinds individuals to their true spiritual condition and prevents them from recognizing the need for God's grace. Paul echoes this sentiment in Philippians 3:9, where he states that his desire is to be found in Christ, not having his own righteousness, which comes from the law. This underscores the central tenet of Reformed theology that salvation is entirely a work of God's grace, and any attempt to achieve righteousness apart from that grace inevitably leads to condemnation.