How do we know that God chooses to show mercy?

God's choice to show mercy is based on His eternal covenant of grace, which was established before the foundation of the world. This covenant involves the Father promising to save a chosen people through the sacrificial work of His Son. Just as David showed mercy to Mephibosheth for Jonathan's sake, God extends His mercy to His elect for Christ's sake, fulfilling the promises made in the covenant. The assurance of our salvation and God's mercy does not depend on our actions or worthiness but entirely on God's sovereign choice and His promise to redeem His people.