Who is Pen Pal from Dog Sees God: Confessions of a Teenage Blockhead and what is their importance?

Throughout the play, CB writes a long letter to his pen pal without expecting a response; however, at the end of the play, his pen pal finally writes back, encouraging CB to be strong in tough times and writing about where he lives, presumably the afterlife, and a new boy moving in who would appear to be Beethoven who seems to be taking care of CB's dog. CB's pen pal signs his letter CS, likely an allusion to Charles M. Schulz, the creator of the "Peanuts" comic strip.