How do we know that grace alone is sufficient for salvation?

We know grace alone is sufficient for salvation through biblical doctrine and the finished work of Christ. Romans 3:24 states, 'being justified freely by His grace through the redemption that is in Christ Jesus.' This indicates that justification before God is solely based on grace. Furthermore, attempting to add works to grace nullifies its effectiveness, as emphasized in Romans 11:6, where it states that if it is by grace, it cannot be based on works. Any mix of grace and works undermines the complete and sufficient sacrifice of Jesus Christ.