How do we know the grace of God is crucial for salvation?

In Galatians 2:21, Paul makes a profound statement regarding the significance of grace: 'I do not frustrate the grace of God: for if righteousness come by the law, then Christ is dead in vain.' This highlights that the grace of God is indispensable for salvation. If we could achieve righteousness through our own efforts under the law, then the sacrificial death of Christ would be unnecessary and meaningless. Therefore, recognizing and embracing grace is essential for understanding our need for a Savior.