For astonishment at the catch of fish they had made seized him and all those with him, and likewise James and John, the sons of Zebedee, who were partners of Simon. Jesus said to Simon, “Do not be afraid; from now on you will be catching men.” When they brought their boats to the shore, they left everything and followed him.
The crowd was pressing in on Jesus, so He got into one of the boats, and continue teaching the crowd from the boat. Notice that boat in the bible often represents the church community, so it's significant that He chose to get into Simon's boat to continue His teaching. It is interesting the sequence of things Jesus did: He taught from Simon's boat, asked Simon to lower the nets for a catch, and lastly called him to become a fisher of men.
Simon, who probably was amazed by His teaching as much as the crowd, called Jesus ‘Master' and followed His command to lower the nets, though he should be more experienced in fishing than Jesus, and he had worked hard all night without catching anything.
Then, after seeing the miracle of catching a great number of fish, Simon was overwhelmed by His power and goodness, he fell down and said to Jesus, “Depart from me, Lord, for I am a sinful man.” At this point he knows Jesus is very special and His goodness reminds him of his sins, that he is not worthy. Nevertheless, Jesus chose him to be a fisher of men, and along with a few others, Simon left everything and followed Him.
This bible passage shows that Jesus does not call perfect people to follow Him, but those who are willing to listen and obey. Simon admitted he was sinful and had second thoughts about what Jesus said, but what's important is that he eventually obeyed the Lord's commands. It is not easy for us when we look at the reality in front of us, but Simon showed us that all we need to do is trust in our Lord, and we'll be amazed as much as he did.