Catechism of the Catholic Church

The coming of God's Son to earth is an event of such immensity that God willed to prepare for it over centuries. He makes everything converge on Christ: all the rituals and sacrifices, figures and symbols of the "First Covenant." He announces him through the mouths of the prophets who succeeded one another in Israel. Moreover, he awakens in the hearts of the pagans a dim expectation of this coming. (711, 762)