Jesus is the Word made Flesh. Jesus is the Bread of Life. Jesus is the Victim offered for our sins on the Cross. Jesus is the Sacrifice offered at the Holy Mass For the sins of the world and mine.
This process may seem very circular, but given their assumptions -- namely, that Jesus is central to God's plan, that God spoke through prophets who might not understand their own words ...
To confirm that Jesus was the Messiah sent from God ... while the fulfilment in the New Testament is God keeping his word. This means that Christians know they can trust God in all things.