The New Testament is really about Jesus Christ. All the Old Testament leads up to the coming of Jesus Christ who is described in the Catechism—“Mediator and Fullness of All Revelation” (65-72).
“In many and various ways God spoke of old to our fathers by the prophets, but in these last days he has spoken to us by a Son.” (Hebrews 1:1-2)
This final and comprehensive intervention by God begins with the Annunciation of the Angel Gabriel to the young Mary of Nazareth. The gist of the message is “Will you consent to be the mother of God’s Son?” Since Mary had resolved to remain a virgin, she did not know how to respond. Her dilemma was solved when she learned that Joseph, to whom she was engaged, would not be the father but God Himself. The same message later was given to Joseph which put his question about her pregnancy at rest.
After the usual nine months of pregnancy, Mary gave birth to a baby boy who was like us in every way except for no sin because He was God and human at the same time. He grew up like any child while living with Mary and Joseph in Nazareth.
Although He became one of us in order to save us from our sin, He lived for thirty years in the hidden life of Nazareth before He spent the last three years of His life in traveling around Palestine and preaching about what He really came to earth to do—namely, to save us and establish His Church that would continue His work after He rose from the dead and returned to heaven.
The new Catechism requires about 700 pages to develop a presentation of the significance and meaning of what Jesus taught and why during those thirty-three years while He lived among us, taught and preached, suffered and died and rose from the dead to ascend into heaven to be with His Father and the Holy Spirit who is the Third Person of the Blessed Trinity. Yes, as you know, there is one God with three persons, the Father, the Son (Jesus Christ ) and the Holy Spirit. More about all of that later.