We see that Simon (Peter) and Andrew first follow Jesus (John 1:37–51). However, now they must follow him day and night. They can no longer continue to do their ordinary work, as in the time when they were John’s disciples. That was the custom in those days: people from Israel chose a certain teacher (rabbi) but kept their daily work for their livelihood.
18 While walking by the Sea of Galilee, he saw two brothers, Simon (who is called Peter) and Andrew his brother, casting a net into the sea, for they were fishermen.