How do we know God's mercy for Christ's sake is true?

The veracity of God's mercy for Christ's sake is grounded in the covenant made between God the Father and His Son, which was established before the foundation of the world. This covenant entails God's commitment to show kindness and mercy to His chosen people, not based on their works or worthiness, but solely for the sake of Christ's redemptive work. As described in Ephesians 1:4-5, God chose us in Christ before the world's creation, revealing the profound truth that all salvation is rooted in His eternal plan for redemption through His Son.