I might discern and distinguish what a difference there is between presumption and confession,— between those who saw whither they were to go, yet saw not the way, and the way which leads not only to behold but to inhabit the blessed country.
In his Confessions, Augustine writes that it was God’s pleasure that he studied Platonism before being touched by Him though the Scriptures. Of all philosophies, Platonism is one that most approximates Christianity, so the former serves to prepare his mind for the latter. But more importantly, familiarity with both enables him to discern the preeminence of Christianity over philosophy.
Plato teaches that true virtue of Man is to become righteous like God, but how such virtue can be acquired he does not say (though he intimates it is a gift of God); Christ proclaims, “I am the way, the truth, and the life. No one comes to the Father except through Me.”
For this is the Mediator between God and men, the man Christ Jesus. For it is as man that He is the Mediator and the Way. Since, if the way lieth between him who goes, and the place whither he goes, there is hope of his reaching it; but if there be no way, or if he know not where it is, what boots it to know whither he should go? Now the only way that is infallibly secured against all mistakes, is when the very same person is at once God and Man, God our end, Man our way
(City of God XI)
The difference between Platonism and Christianity is not merely that of interpretation, but the difference between perception/speculation on one side, and reality/true knowledge on the other. To use a Biblical imagery, there is a great gulf fixed between them. It is the difference between death and Life. Though philosophy may delight man with a magnificent picture of truth and beauty, it is nevertheless dead, and so the greatest philosophical Idea cannot be compared with the least life-giving word of God.
Had I first been moulded in Thy Holy Scriptures, and hadst Thou, in the familiar use of them, grown sweet unto me, and had I afterwards fallen upon those volumes, they might perhaps have withdrawn me from the solid ground of piety; or, had I stood firm in that wholesome disposition which I had thence imbibed, I might have thought that it could have been attained by the study of those books alone.
If Augustine had come across Platonism after having been familiar with Christianity, it might have withdrawn him “from the solid ground of piety”, for the former does present an attractive image of the reality with which a Christian is familiar, as images projected on the wall might deceive people into thinking they are real; however, since he started with Platonism, he was well aware of its limitations, and knew that it was but a shadow, and therefore did not mistake the shadow for substance, i.e., the Truth to be found in Christ alone.