I think I know why, but I’m guessing. Why dose the Pope pick a new name to go by? Was there a time when they didn’t go by a new name?
Yes, there was a time when popes retained their baptismal names.
Supposedly following Sergius I, the new pope was named Boca di Puerco (Pig’s Mouth)–and changed his name to the more dignified Sergius II.
Most popes have followed suit since.
Why did Christ rename Simon once he handed him the keys to the kingdom of Heaven?
well he named him “Rock”. That was what I was thinking it had to do with. But didn’t know if St. Linus was a chosen name when he became Pope.