How do we know God does not change?

The doctrine of God's immutability posits that God does not change in His nature, will, or promises. This truth is encapsulated in Malachi 3:6 where God declares, 'For I am the Lord, I change not; therefore ye sons of Jacob are not consumed.' This assurance underlines the reliability of God’s eternal promises and His commitment to His covenant people. God exists outside of time and is unaffected by the changes of creation, maintaining His perfect holiness and righteousness throughout all generations.