Matthew 5:17
Think not that I have come to abolish the law and the prophets; I have come not to abolish them but to fulfil them.
St. Augustine famously observed that the New Testament is hidden in the Old Testament and the Old Testament is only fully reveal in light of the New Testament. This is the "Great Apostolic Forehead Smack Principle". John notes that the apostles still did not understand from the Scripture that Jesus had to rise from the dead, even when they were standing at the mouth of the empty tomb. They did not even understand it when they met the Risen Christ on the road to Emmaus. It took the celebration of the Eucharist for their eyes to be opened and for them to smack their foreheads and realize that the death and resurrection of the Messiah and his saving gospel had been staring them in the face the whole time but they hadn't seen it. This is why the Church has always read its Bible (Old and New Testament) at the celebration of the Eucharist: because the Holy Spirit still lurks in the book he inspired and awaits the change to surprise us again. The New Testament doesn't cancel the Old: it makes it come true.
