I'm still working out what the significance of this is, but I'm now surer than ever:
In season 2, Aziraphale's bookshop is the Garden of Eden.
What first tipped me off was the end of 2x01, when Gabriel asks about Outside, and Crowley urgently warns him that he needs to stay inside the bookshop. It reverberated against the themes of season 1, where choosing freedom over safety is symbolised by Leaving the Garden. Supporting this connection, one of the songs on the season 2 soundtrack is called Leaving the Bookshop; it plays in 2x06 when Crowley escorts Nina and Maggie outside.
There's an even clearer indicator of the symbolism, though, and I am so fascinated by the implications. When Gabriel first arrives at the bookshop in a state of undress, one of the things he says to Aziraphale is:
"Who told you I was naked?"
It's a funny line but it's also surprisingly biblically significant. In Genesis, Adam and Eve's loss of innocence after eating the fruit of knowledge is shown by their realisation they are naked. In this scene, Gabriel is like them before this transgression, innocent and unconscious of his own nakedness.
But it's even more on the nose than that, because in Genesis, when God appears to Adam after he eats the fruit, Adam hides, and then admits he's afraid because he's naked. And I quote directly, Genesis 3:11 (New International Version):
And [God] said, “Who told you that you were naked? Have you eaten from the tree that I commanded you not to eat from?”
I'm sure this reference is intended. It's too similar to be a coincidence. So Gabriel's memory loss is comparable to the innocence that preceded the Fall of Man, and that's fascinating in its own right. This also makes the bookshop, where he is protected so long as he stays inside its walls, a clear parallel to Eden.
In relation to Gabriel, I think Beelzebub is Eve, offering Adam the knowledge of good and evil in the form of a fly holding his hidden memories. An argument could be made that they are the serpent to his Eve, but I think the partnered dynamic makes this a more fitting interpretation.
I'm still thinking on the roles that Crowley and Aziraphale play in this analogy. I keep coming back to Gabriel's line, "I don't go outside, and now I have two friends." If this is Eden, who are his friends? Are Crowley and Aziraphale reprising their roles as the serpent and the guardian? Are they God and Satan playing games with their own little universe, perhaps? Or are they Adam and Eve?
Obviously, if the bookshop is Eden, this has major implications for Crowley and Aziraphale too in the context of their break up. With this framing, Crowley telling Aziraphale, "You can't leave this bookshop" becomes a fascinating twist on his traditional role. He's asking Aziraphale to stay with him in blissful ignorance, rather than confront the truth of their world. I'm not arguing that this is the only level at which this line should be read, but it's one that's worth considering.
You may also notice that in light of this biblical reference, "Who told you I was naked" becomes the first time amnesiac Gabriel echoes the words of God. I'm really not sure what these echoes mean, but they sure do intrigue me.