A few years ago Pope Benedict XVI gave a series of lectures on the early church fathers, and they have been collected into a book: Church Fathers: From Clement of Rome to Augustine. In one of the lectures on St. Augustine, the Pope mentioned something significant about Ambrose’s influence on St. Augustine:
The great difficulty with the Old Testament, because of its lack of rhetorical beauty and of lofty philosophy, was resolved in Saint Ambrose’s preaching through his typological interpretation of the Old Testament: Augustine realized that the whole of the Old Testament was a journey toward Jesus Christ. Thus, he found the key to understanding the beauty and even the philosophical depth of the Old Testament and grasped the whole unity of the mystery of Christ in history as well as the synthesis between philosophy, rationality, and faith in the Logos, in Christ, the Eternal Word who was made flesh. (171)
Interesting Biblical Theology via a typological interpretation of the OT was part of the breakthrough for St. Augustine in understanding the Scriptures. The Old Testament is a way to Jesus Christ, the eternal Word made flesh.