What does the Bible say about God's mercy and hardening?

The Apostle Paul, in Romans 9:18, expresses a profound truth about God's character: 'Therefore hath he mercy on whom he will have mercy, and whom he will, he hardeneth.' This declaration emphasizes God's absolute sovereignty in both showing mercy and executing judgment. Throughout Scripture, examples abound of God's prerogative in extending mercy or hardening hearts, clearly affirming that these choices belong solely to Him. We see this illustrated in various accounts, such as God's conversation with Moses in Exodus 33, where He declares, 'I will be gracious to whom I will be gracious, and will show mercy on whom I will show mercy.' Thus, God's decisions are not contingent upon human action or worth but are rooted in His divine will.