What was the real historical event?
What God has chosen to reveal concerning the origins of the human race, the first couple, the command he gave them, and Adam and Eve’s disobedience, is set down by the inspired sacred writer in Genesis, and beyond this we cannot go. The only knowledge we have and which God was pleased to reveal concerning the point in question is what the sacred writer has set down in scripture. The whole biblical narrative concerning the point in question concerns profound truths and mysteries. We must keep in mind here we are dealing with the inspired word of God and divine revelation.
There is nothing preventing anyone or any catholic from believing in the literal interpretation of the biblical narrative of Adam and Eve in the garden of Eden or paradise. Such a person would be in good company here. Probably most of the Israelites before Jesus, the jews at the time of Jesus, the Apostles, and many fathers, doctors, and saints of the Church believed in the literal interpretation of the garden of Eden episode.
It is not against the catholic faith, the teaching of the Church, sound reason, any certainty from science, nor against the literal text itself of Scripture to believe in the literal interpretation of Adam and Eve in the garden of paradise and what follows and such is the interpretation I follow. There are at least some truths involved here that the Church tells us are a matter of faith and that requires our assent; it’s a matter of divine revelation. Are there solely metaphorical elements involved here? Perhaps, though there is no certainty in this. (Some of the passages involved definitely have a spiritual meaning and sense but this does not entail that they don’t have a literal sense too. Scripture can have a multiplicity of senses). It may be possible that a catholic can hold the opinion that there may be some solely metaphorical elements concerning the point in question; which points exactly or which passages of Scripture involved I don’t think the Church has declared and which it may never declare. At the same time, though it may be possible for a catholic to hold to the opinion that there are some metaphorical elements involved, the truths underlying these so-called metaphorical elements must be held with catholic faith. For example, it may be possible for a catholic to hold that the command God gave to Adam and Eve to not eat of the tree of the knowledge of good and evil is metaphorical. Not the command itself, but the image of the tree. That God gave Adam and Eve a command and that Adam and Eve disobeyed the command requires catholic faith; this is of divine revelation.
The fact of the matter is, is that no one can say with certainty from what has been revealed to us through the word of God, that God did not plant a garden in which he placed the first couple, Adam and Eve, or that there was not a real material tree called the Tree of Life or a real material tree called the Tree of the knowledge of good and evil (presumably a fruit tree of some kind) that God told our first parents not to eat of. Again, this whole narrative involves profound mysteries and truths.
For example, not a few fathers, doctors, and saints of the Church consider the Tree of Life as a figure of Christ. The phrase ‘tree of life’ appears in other passages of Scripture as well. In Deuteronomy 30:19, in giving the commandments from God to the Israelites Moses says “I call heaven and earth to witness against you this day, that I have set before you life and death, a blessing and a curse”. This seems to be a hearkening back to Adam and Eve in the garden of paradise. In the midst of the garden (right before the very eyes of our first parents) was the Tree of Life and the Tree of the knowledge of good and evil, i.e., life and death. At least some fathers and doctors of the Church see the manner of Christ’ death, namely, dying on the wood or tree of the cross as paying back what Adam and Eve took from a tree. In response to the question whether Christ should have suffered death on a cross, St Thomas Aquinas says:
"I answer that, It was most fitting that Christ should suffer the death of the cross… Secondly, because this kind of death was especially suitable in order to atone for the sin of our first parent, which was the plucking of the apple from the forbidden tree against God’s command. And so, to atone for that sin, it was fitting that Christ should suffer by being fastened to a tree, as if restoring what Adam had purloined; according to Psalm 68:5: “Then did I pay that which I took not away.” Hence Augustine says in a sermon on the Passion [Cf. Serm. ci De Tempore]: “Adam despised the command, plucking the apple from the tree: but all that Adam lost, Christ found upon the cross.”’ (Summa Theologica) We don’t need to take the mention about the apple literally here. Genesis does not mention what kind of fruit tree the forbidden tree was. Aquinas knows this very well. Augustine speculated that it was an apple tree but he doesn’t usually speculate without a reason and a scriptural reason at that.)
Things in the Old Testament that may be figures of realities in the New Testament or of Christ does not entail that these figures in the Old Testament were not real or not historical. On the contrary, I think we need to generally assume the historical reality of the figures if they are to be figures at all of New Testament realities. For example, the Passover supper before the Israelites left Egypt is a figure of the Eucharist and the passion of Christ. The passing through the Red Sea is a figure of baptism (St Paul in Corinthians I believe).