From Vatican.va, an excerpt from the teachings of Pope Benedict XVI  General Audience 2007

Until that moment, Ambrose had been the most senior magistrate of the Empire in northern Italy. Culturally well-educated but at the same time ignorant of the Scriptures, the new Bishop briskly began to study them. From the works of Origen, the indisputable master of the “Alexandrian School”, he learned to know and to comment on the Bible. Thus, Ambrose transferred to the Latin environment the meditation on the Scriptures which Origen had begun, introducing in the West the practice of lectio divina. The method of lectio served to guide all of Ambrose’s preaching and writings, which stemmed precisely from prayerful listening to the Word of God. The famous introduction of an Ambrosian catechesis shows clearly how the holy Bishop applied the Old Testament to Christian life: “Every day, when we were reading about the lives of the Patriarchs and the maxims of the Proverbs, we addressed morality”, the Bishop of Milan said to his catechumens and neophytes, “so that formed and instructed by them you may become accustomed to taking the path of the Fathers and to following the route of obedience to the divine precepts” (On the Mysteries 1, 1). In other words, the neophytes and catechumens, in accordance with the Bishop’s decision, after having learned the art of a well-ordered life, could henceforth consider themselves prepared for Christ’s great mysteries. Thus, Ambrose’s preaching – which constitutes the structural nucleus of his immense literary opus – starts with the reading of the Sacred Books (“the Patriarchs” or the historical Books and “Proverbs”, or in other words, the Wisdom Books) in order to live in conformity with divine Revelation.

It is obvious that the preacher’s personal testimony and the level of exemplarity of the Christian community condition the effectiveness of the preaching. In this perspective, a passage from St Augustine’s Confessions is relevant. He had come to Milan as a teacher of rhetoric; he was a sceptic and not Christian. He was seeking the Christian truth but was not capable of truly finding it.
What moved the heart of the young African rhetorician, sceptic and downhearted, and what impelled him to definitive conversion was not above all Ambrose’s splendid homilies (although he deeply appreciated them). It was rather the testimony of the Bishop and his Milanese Church that prayed and sang as one intact body. It was a Church that could resist the tyrannical ploys of the Emperor and his mother, who in early 386 again demanded a church building for the Arians’ celebrations. In the building that was to be requisitioned, Augustine relates, “the devout people watched, ready to die with their Bishop”. This testimony of the Confessions is precious because it points out that something was moving in Augustine, who continues: “We too, although spiritually tepid, shared in the excitement of the whole people” (Confessions 9, 7).