The final division of philosophy--moral philosophy--is that question of the highest good (the summum bonum), which is either a matter of the body, or of the soul, or both. What Plato brings to the philosophical table is the understanding that this highest good cannot ultimately come from man, but must come from God. "Therefore he did not doubt that to philosophize is to love God, whose nature is incorporeal. Whence it certainly follows that the student of wisdom, that is, the philosopher, will then become blessed when he shall have begun to enjoy God. "
Whether people who believe something like this are called "Platonists" or by some other title, they are the philosophers who come closest to what Christians believe.
Unfortunately, the closest thing to heaven is hell. What the Platonists and other philosophers have bent all their intellect on finding, the simplest, most poorly educated man who is a true believer already has--knowledge of and a relationship with the infinite, eternal, and holy Creator of the universe.
This, therefore, is the cause why we prefer these to all the others, because, whilst other philosophers have worn out their minds and powers in seeking the causes of things, and endeavoring to discover the right mode of learning and of living, these, by knowing God, have found where resides the cause by which the universe has been constituted, and the light by which truth is to be discovered, and the fountain at which felicity is to be drunk.Augustine is going to engage with the Platonists because they are the most well known and highly regarded of the pagan philosophers, but this is not to be confused with saying that Plato has arrived at a saving true. Just that Plato is the most known and respected.