On Sundays, Augustine recalls, he would come to listen attentively to Ambrose’s sermons. People talked and interrupted, as we can infer from Ambrose’s own words, but Augustine was not troubled. He was not there to take in the contents, and yet as he listened to the style, his ‘heart’, typically, opened to what was being spoken. He does not recall that he was influenced by Ambrose’s rhetorical training, one which he shared. Instead, he is clear, as we should be, that Ambrose was the first person to show him that concealed other meanings, or allegories, could be discerned in awkward verses of scripture. They did not have to mean what they appeared to say on the surface. Ambrose’s use of allegory was derived from Greek authors, the Christian thinker Origen (c.185–254) and the Greek-speaking Jew Philo in Alexandria in the early to mid-first century, from whose books Ambrose took whole patterns of interpretation while claiming that, as a Jew, Philo had not been able to ‘discern the mystery’ himself.27
Hidden meanings and ‘mysteries’ beneath the surface of a text were not new for Augustine. During his literary training he had learned that allegory could be applied to verses by Virgil.28 Now, beneath the clumsy style of the Latin scriptures, a deeper meaning was being shown to lie hidden. Ambrose could reveal its depths because a key had been made available by Christ. ‘You have read in the Apocalypse,’ Ambrose later wrote, ‘that the Lamb opened the sealed book which nobody thitherto had been able to open… by means of His Gospel: Jesus handed over the key of knowledge and gave it to us so that we may open.’ Faith in Christ, Ambrose believed, guides scripture’s readers to the hidden meanings which unify it and to which they are linked by the Holy Spirit. In this sense, so Ambrose would preach, ‘the Letter kills, the Spirit gives life’, words of St Paul to the Corinthians which greatly struck his hearer, Augustine.29 They were a sort of ‘rule’ for understanding scripture whose depths of meaning made it like a ‘sea’. One level might be natural, but another might be ‘moral’, discernible with the help of allegorical keys. A third level was mystical, which only allegory could unlock. Ambrose did not name his source, but, like the ‘rule’, these three levels had been formulated in Greek by Origen.30
Fox, Robin Lane. Augustine: Conversions to Confessions . Basic Books. Kindle Edition.
Note, the author Robin Lane Fox is an atheist.
But he is a quite good scholar.
Contrast this to Tarazi, “Chrysostom on Isaiah: A Paradigm for Hearing Scripture”. According to that article John Chrysostom understood allegorical interpretations to be idolatrous.