Wilbur Mercer

Rick decides to climb up a wall in chapter 21. But he soon comes to realization that after climbing up, the hill had changed him making him feel a certain kind of way that he never felt before. Even though Inspector Bryant was unavailable at the time, Rick talks to Miss Marsten about the feeling that he felt during his trip up/down the hill by stating that he felt “permanently fused with him.”

“But if I’m Mercer, he thought, I can never die, not in ten thousand years. Mercer is immortal.” (Chapter 21)

In chapter 21, you can see Rick go through a transformation after he returns from climbing up the hill. My question is, how did that particular experience on the hill change him?