James and John, the sons of Zebedee, were fishermen on Lake Tiberias. They followed the teaching of John the Baptist. So when the Baptist pointed to Jesus of Nazareth one morning and said, "This is the Lamb of God", John followed him. When Jesus said to the two brothers who were casting their nets, "Come with me", James and John followed him.
John had a great love for Christ. He thought that Christ's love was even greater. So he was called "the disciple whom Jesus loved". He is on Mount Tabor at the Transfiguration, at the Last Supper and on Calvary, the only one among the apostles, at the foot of the cross. It was there that Jesus entrusted Mary, his mother, to him.
According to an ancient tradition, John later lived with Mary in Ephesus. That he wrote the Fourth Gospel there. That a stay on Patmos was the occasion of a revelation that became the Apocalypse.