what is significant in the rebirth motif at the beach?

Gene experiences a rebirth when he realizes that Finny calls him his best friend, but he can't return the favor.

Gene, "was stopped by that level of feeling, deeper than thought, which contains the truth."

This realization was a rebirth. Gene knows what Finny wants, and because of this he's free to be himself again...... no strings, no ties; he can just live. The two of them aren't out of the woods yet though....... there's still quite a bit of story here.