How do we know that the covenants of God are fulfilled in Christ?

Paul explicitly explains in Galatians 3:16 that the promises made to Abraham and his descendants were ultimately directed towards one specific descendant, Christ. This underscores that the Old Covenant, including the Sinai covenant, served to preserve Israel until Christ arrived, who would fulfill all promises made. Consequently, once Christ accomplished His work, the physical distinctions and representations of the old covenant were rendered obsolete, as the true fulfillment of God’s promises rests in the redemptive work of Christ alone. This understanding reaffirms that the church, as the body of Christ, is the culmination of God's redemptive plan.