Following his two principles for the interpretation of Sacred Scripture, Augustine, in my judgment, succeeded in demythologizing Genesis 1 in the fourth century A.D. The literal, fundamentalist reading of that text and the acceptance of that literal reading as containing the factual truth about God's creation of the cosmos makes an utter mockery of the Jewish, Christian, and Muslim belief in the doctrine of creation ex nihilo by God.
According to Augustine's understanding of God as a purely spiritual being having eternal (i.e., nontemporal and immutable) existence, Genesis 1 cannot be interpreted as a succession of creative acts performed by God in six temporal days. In Augustine's view, the creation of all things was instantaneously complete. God created all things at once in their causes. The actualization of the potentialities invested in those original causes is a natural development in the whole span of time.
If Augustine were writing in the twentieth century, he would have called it an evolutionary development. The order of "six days" is not a temporal order but an order of the graduations of being, from lower to higher. In thus interpreting Genesis 1 in the light of twentieth-century knowledge of evolutionary development, Augustine would be following his own two rules for (1) holding on to the truth of Sacred Scripture without wavering, but also (2) holding on to an interpretation of it only if that accords with everything else now known.
Demythologizing Genesis 2 and 3 is more difficult. What Augustine did with Genesis 1, someone must do with Genesis 2 and 3. If they are Christians, they must interpret the story so that it preserves basic Christians beliefs: about the moral state of the human race, a state that requires a redeemer and a savior for the salvation of the soul and the resurrection of the body. The narrative in Genesis 2 and 3 must be read so that its exegesis supports the Christian belief that God, in creating man in his own image, endowed him with free will and, thereby, with the choice between obeying or disobeying God's commandments.
The story of the Garden of Eden, of Adam and Eve and of the serpent and Lillith, may be a myth rather than true history, but this does not alter the religious significance that must be found in it when it is properly interpreted in nonnarrative terms. That is the task of the biblical exegete when he attempts to preserve the religious doctrine while removing the mythology. Demythologizing Sacred Scripture calls for profoundly daring biblical exegesis, that dares to be true to the two precepts that Augustine himself followed in demythologizing Genesis 1.
Mortimer J. Adler, Truth in Religion, pp. 65-66