How do we know that grace and works can't mix?

The Apostle Paul emphasizes the incompatibility of grace and works in Romans 11:6, where he asserts that if salvation is obtained by grace, it cannot be earned through works, or else grace ceases to be grace. This means that any attempt to complement God's grace with personal merit nullifies the very essence of divine grace. Salvation is a free gift from God, given not based on human efforts but solely upon His sovereign will and love. Therefore, it is vital for believers to rest in the assurance of grace rather than seeking to earn God's favor through their deeds, which would ultimately lead to futility and despair.