I have wondered and even wrote a fanfic about what Aslan said to Edmund after his rescue. I think I wondered so much because I've always connected to Edmund and his journey, and he's the Pevensie child I relate to the most. This conversation seems to be such a pivotal moment in Edmund's life that I do find myself reflecting on what Aslan could have said to Edmund that could be so transformative to Edmund. To me, there is nothing wrong with readers being curious as long as it is done in the spirit of compassion/sympathy for Edmund and a desire to better know and understand Aslan rather than in a spirit of nosy gossiping. Personally, I suspect that the fact that we aren't told exactly what Aslan said to Edmund gives us a chance to imagine what Aslan would say to us in Edmund's position. So in a way, it is an invitation for us to place ourselves in Edmund's situation and to empathize with Edmund and to perhaps have our own experience with Aslan's grace. So I like the fact that there is the space for each individual reader to speculate or not speculate on what is said as the reader chooses.
I think what the reader does see is enough to know that the conversation had a transformative effect on Edmund. That it was redemptive and restorative for him. That it was an encounter with grace and mercy and likely justice for him. After all, Edmund will be known as King Edmund the Just. Perhaps some of Aslan's discussion with Edmund is about the nature of justice. I could see that really resonating with Edmund.
Anyway, I imagine that it would be a very profound conversation. Painful and humbling for Edmund in some parts, but also gentle and encouraging. And I believe that by the end of it, Edmund would emerge with a clear understanding of how much Aslan loves him.
I think the privacy of the conversation between Edmund and Aslan really shows the privacy and intimacy that believers in God can have in their conversations with God through prayer. It is sometimes in these most private, intimate moments with God that we can be at our most vulnerable and be our truest selves so I like that C.S. Lewis leaves spaces for characters like Edmund to have those very private and very important, transformative conversations with Aslan.
I think it also shows the uniqueness of Edmund's relationship with Aslan. Aslan and Edmund had at least this one conversation that nobody else would have with Aslan. That is like how everyone has their own relationship with God, and for each of us, there are these private conversations with God to which nobody else is invited but can be some of the most beautiful conversations we have with God.
That is my view, basically.
Do I think it wrong to speculate on Aslan's conversation with Edmund? No, because at least for me, it was a graceful exercise where I thought about my own relationship with God and had a little dialogue with God myself that was both humbling and encouraging for me. Speculating on Edmund's relationship with Aslan built my own relationship with God. I am sure if I told C.S. Lewis that he'd be happy to hear it.
Do I think it was wrong for C.S. Lewis not to include the conversation in the story? No, because I think it did give readers like myself a chance to speculate if we wanted and to maybe grow in our own relationships with God.
Sorry for the rambling post. Hopefully some of it makes sense.