Matthew 4:16-20
Mat 4:16 (KJB)
The people which sat in darkness saw great light; and to them which sat in the region and shadow of death light is sprung up.
(Isa 9:2 KJV) The people that walked in darkness have seen a great light: they that dwell in the land of the shadow of death, upon them hath the light shined. That great light which these people saw was God the Son. When Isaiah had penned his prophecy, it was probably the darkest time for the region around Galilee. Jesus would minister there and bring the light to the Gentiles. (Isa 49:6 KJV) And he said, It is a light thing that thou shouldest be my servant to raise up the tribes of Jacob, and to restore the preserved of Israel: I will also give thee for a light to the Gentiles, that thou mayest be my salvation unto the end of the earth.
Mat 4:17 (KJB)
From that time Jesus began to preach, and to say, Repent: for the kingdom of heaven is at hand.
Here we have Jesus continuing to bring the same message which John brought concerning repenting because the kingdom of God was at hand. Temporarily Jesus had carried on the ministry of John until such a time that He would reveal Himself as the Messiah when He would start to do miracles. Since John was now cast into prison, the people would continue to know that the rule of God was near. Jesus was able to proclaim this because He is the King and Son of God.
Mat 4:18 (KJB)
And Jesus, walking by the sea of Galilee, saw two brethren, Simon called Peter, 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.
Mat 4:19 (KJB)
And he saith unto them, Follow me, and I will make you 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;
Mat 4:20 (KJB)
And they straightway left 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.