Mark 1:16

And passing along by the sea of Galilee, he saw Simon and Andrew the brother of Simon casting a net into the sea; for they were fishers. And Jesus said unto them, Come ye after me, and I will make you to become fishers of men. And straightway they left the nets and followed him.

THE CALLING OF FOUR APOSTLES

This was not the first meeting of Jesus with these disciples; for the apostle John gives details of their first meeting in his gospel (John 1:35-51). The reference here is to a more formal calling to the apostleship and involved their leaving their occupation to attend Jesus continually.

For they were fishers ... These words figure prominently in the allegations regarding the priority of Mark; but it should ever be remembered that the extensive oral traditions of the early church were available to all the gospel writers, and that certain set expressions, as this, derived from common usage throughout the church and not from one writer's reliance upon a document written by another. The notion that Matthew copied Mark leads to the supposition that one of the apostles, such as Matthew, who was an eyewitness to all that Jesus did, and who had orally taught the gospel to countless Christians throughout the world of that era, and who was one of the group of men whose words formed the oral traditions which prevailed in the first two or three decades of the Christian era ... the incredible supposition that such an author would have needed to consult Mark is ridiculous and is in no wise proved by such expressions common to two, or even three, of the synoptics. The necessary existence of oral traditions before any of the gospels was written is a more than sufficient explanation of the common expressions such as this.

Fishers of men ... This purpose of the Master to make the men here mentioned to be "fishers of men" indicates this as a more formal call to the apostleship, contrasting with the first meeting recorded in John. They promptly obeyed the call.