It's like asking "Why Jesus became the messiah?". Well, it's a very difficult question and answers may vary depending who you ask.
Why Did Simon Become A Disciple?
Simon is none other than Saint Peter. He was one of the Twelve Apostles of Jesus. He was one of those people who were chosen by Jesus himself to be his original disciple. His life and his preaching are attributed in the New Testament Gospels and the Acts of Apostles. Before he became a disciple of Jesus he was a Galilean fisherman.
There is story in Bible which says that Jesus cured Simon's mother-in-law from some ailment. This healing act made Simon believe in Jesus. Later when Jesus was resuming his journey he literally called Simon and his brother Andrew to accompany him and in his own words stated, "Follow me, and I will make you fishers of men". Simon became Jesus's follower on that day and became his most revered disciple. Jesus himself gave him the name Cephas which means rock. Thus Jesus called Simon "his rock".
There is story in Bible which says that Jesus cured Simon's mother-in-law from some ailment. This healing act made Simon believe in Jesus. Later when Jesus was resuming his journey he literally called Simon and his brother Andrew to accompany him and in his own words stated, "Follow me, and I will make you fishers of men". Simon became Jesus's follower on that day and became his most revered disciple. Jesus himself gave him the name Cephas which means rock. Thus Jesus called Simon "his rock".