How do we know Christ fulfills God's promises?

Christ's fulfillment of God's promises is evidenced by His resurrection and glorification. Isaiah 55 mentions the everlasting covenant and the sure mercies of David, which are guaranteed through Christ. Ephesians 1 elaborates on this by celebrating His resurrection power and His headship over the church. As believers, we can rest assured that His promises to save and keep His people are certain because He has accomplished the work required for our salvation through His life, death, and resurrection, affirming our justification and eternal security.