How does the Bible explain God's mercy and justice in election?

In Romans 9:15-16, Paul makes clear that God's mercy is not arbitrary but is a sovereign choice. God states, 'I will have mercy on whom I will have mercy,' indicating that His decisions are rooted in His character and purpose, entirely justified within the context of His divine will. While God extends mercy to the elect, He also allows others to continue in their rebellion and ultimately face justice for their sins. This dual aspect of God's nature—mercy towards the elect and justice towards the reprobate—highlights His righteousness. Every person receives what they deserve; those who are shown mercy receive grace they do not deserve, while those who are not chosen face the consequences of their rebellion against God. This sovereign orchestration by God assures that His glory is displayed in both salvation and judgment.