What does the Bible say about frustrating the grace of God?

In Galatians 2:21, Paul makes a critical statement: "I do not frustrate the grace of God; for if righteousness come by the law, then Christ is dead in vain." This teaches us that any attempt to gain righteousness through the law undermines the core message of the gospel, which is that salvation is a gift of grace. To frustrate the grace of God means to mix it with human effort or legalism, thus obscuring the truth that salvation is solely through faith in Christ. When we try to earn God's favor through our works or adherence to the law, we are essentially asserting that Christ's sacrificial death was insufficient. Therefore, understanding grace is foundational for true faith and assurance in Christ's fulfillment of the law on our behalf.