What Exactly Was Original Sin?

There are many Christians who concede that the Book of Genesis was metaphorical not literal, but I've never heard any Christian explain exactly what this metaphor represents, specifically the whole business with the apple and the expulsion from Eden. Presumably, since they still believe in original sin, there was some kind of event that got god angry at us for which Jesus needed to be sacrificed in order to save us all from hell, but what was this? What does the metaphor of the apple represent? If this was not a historical account, then what event in history actually did result in this original sin?

Why I Am Not Agnostic

Most Atheists are, in fact, agnostics. They know there is no proof that god does exist, but many will concede that they cannot, in fact, prove that god does not exist either. They simply cite the lack of evidence for god as a reason to not accept the proposition of his existence. I, on the other hand, am convinced of the non-existence of god, or at least they Abrahamic conception of god, because I believe it to be completely incoherent. I, in fact, can't believe it, because it makes no sense.

What I find specifically nonsensical is the idea that god created time, ie. that time and the universe had a beginning, and god is responsible for that beginning. God himself, however, did not have a beginning. This implies that god can exist in a state independent of time. This is incoherent. Time is a necessary condition for existence. Nothing can exist, not even god, in a state in which there is no time. If time had a beginning, then everything that exists also had a beginning, including god.

In order for something to be said to exist at all, it must exist for a period of time. If time had a beginning, how long did god exist before that beginning? Zero seconds, in other words, god did not exist before the beginning of time. The only way the idea of an eternal god, ie, a god without a beginning makes any sense is if time also had no beginning. It is only in an eternal universe that an eternal god makes any sense.