This story's ending packs an emotional punch:
In the early morning on the lake sitting in the stern of the boat with his father rowing, he felt quite sure that he would never die. (65)
How did we go from innocent (and naïve) questions to this sort of definitive conclusion? And why does Hemingway remind us that it's the early morning on the lake when he already told us that the sun was coming up in the last paragraph? And why does the seating chart of the boat matter? So many questions!
First off, let's talk about the dawn as a symbol. A new day means a new start. So at the dawn of this new day Nick is coming out of last night's confusions with a new understanding.
But that understanding isn't a very adult one. Death, or at least Nick's own death, seems impossible to Nick, even though he just witnessed it in another person. But this is his way of resolving the fact that he now has to live in a world where death is a reality. After all, do we go about our daily lives thinking about how we're going to die eventually? Remember, Nick is still a kid who just witnessed death for the first time, and he has to process this new information somehow.
And finally, the fact that Nick's dad is the one rowing the boat, with Nick in the stern (that's a fancy nautical word for the back) shows us that Nick still isn't quite ready to steer the boat himself. He still needs guidance; but even this image seems to foreshadow the fact that Nick is going to one day have to navigate for himself.