Mark 1:16-20

Mark 1:16 (KJB)
Now as he walked by the sea of Galilee, he saw Simon and Andrew his brother casting a net into the sea: for they were fishers.

This meeting with Simon and Andrew was not the first meeting they had with Jesus. John records in John 1:35-42 their first meeting. Both of them were fishermen which had their business on the Sea of Galilee.

(John 1:35 KJV) Again the next day after John stood, and two of his disciples;

(John 1:40-42 KJV) One of the two which heard John speak, and followed him, was Andrew, Simon Peter's brother. {41} He first findeth his own brother Simon, and saith unto him, We have found the Messias, which is, being interpreted, the Christ. {42} And he brought him to Jesus. And when Jesus beheld him, he said, Thou art Simon the son of Jona: thou shalt be called Cephas, which is by interpretation, A stone.

Mark 1:17 (KJB)
And Jesus said unto them, Come ye after me, and I will make you to become fishers of men.

Jesus called them while they were doing their work and told them that He would make them fishers of men. They probably looked at the fish in the boat and immediately identified with what Jesus was saying to them. As they caught a cache of fish, they would now trawl for the souls of people. These two men had been the disciples of John and heard all about repenting and the Kingdom of God being at hand but now they were about to enter into an active part of spreading the kingdom of God to the ends of the earth. Jesus was also telling them that it was time to break away from John and to now follow Him because John was only the forerunner and his ministry was not the permanent one. John preached repentance, Jesus gives repentance. (2 Tim 2:25 KJV) In meekness instructing those that oppose themselves; if God peradventure will give them repentance to the acknowledging of the truth;

Mark 1:18 (KJB)
And straightway they forsook their nets, and followed him.

It did not take them long to realize who was standing there before them and telling them to follow Him. They wasted no time in leaving their fishing business and started following Jesus. This is how Christians are to be. As soon as we become saved, we start following Jesus and we become His disciples. We do not wait years to get involved with ministry but from the first moment on when we are called and saved, we begin our ministries, even if we do not know much but this we would know, that something has happened in our life which has changed us drastically.

Mark 1:19 (KJB)
And when he had gone a little farther thence, he saw James the son of Zebedee, and John his brother, who also were in the ship mending their nets.

While Jesus was still on the shoreline, He saw two others mending or preparing their nets for the next day’s catch. These were the sons of Zebedee which became known as the sons of thunder. (Mark 3:17 KJV) And James the son of Zebedee, and John the brother of James; and he surnamed them Boanerges, which is, The sons of thunder: James would be the first martyr among the disciples. (Acts 12:1-2 KJV) Now about that time Herod the king stretched forth his hands to vex certain of the church. {2} And he killed James the brother of John with the sword. The name “James” is the Greek form of the Hebrew name “Jacob” which means “supplanter.” The name “John” means “the Lord has been gracious.”

Mark 1:20 (KJB)
And straightway he called them: and they left their father Zebedee in the ship with the hired servants, and went after him.

Just as Peter and Andrew did, James and John also left the ship and followed Jesus. The fact that their father is included in this verse shows that they had left not only their business but their families also. James and John must have had a good business going with their father since they also had servants. This is the essence of the calling of a Christian. We may be called upon to not only leave our vocation but also to leave our families and be separated from them, sometimes for life as so many missionaries could attest to. By choosing disciples, Jesus is also showing us that no Christian can be an island and each one needs a support base for their ministry. Not necessarily only financial support but also spiritual and prayer support. It is a body of believers working together, not millions of islands working independently.