How do we know the sure mercies of David are true?

The assurance of the sure mercies of David lies in their fulfillment through Jesus Christ, who is a descendant of David. The Apostle Paul connects these mercies in Acts 13:34 to the resurrection of Christ, affirming that the promises made to David find their completion in Him. Furthermore, the new covenant described in Jeremiah 31 highlights God's commitment to His people, manifesting in the life, death, and resurrection of Christ, which assures believers of their reconciliation and promised mercies.