How do we know that legalism is wrong in Christianity?

Legalism misleads individuals into believing they can achieve righteousness through their own works rather than by the grace of God. Jesus rebuked the Pharisees for their focus on outward actions while neglecting the heart's condition. True faith acknowledges human depravity, understanding that redemption and acceptance before God is solely by grace, as Paul affirms in Galatians 2:21, stating that if righteousness could be gained through the law, then Christ died for nothing. The true believer's confidence must rest wholly on Christ's finished work.