1) "for they were fishers": These two brothers were simple fishermen, yet the Lord Jesus called them, and greatly used them in His gospel ministry. This is especially encouraging to me. Jesus could have called the wisest, the richest, the most highly educated, but He chose to call these two fishermen to be a part of His gospel ministry! "Now when they saw the boldness of Peter and John, and perceived that they were unlearned and ignorant (unschooled, ordinary) men, they marveled; and they took knowledge of them, that they had been with Jesus." Acts 4:13.
"Follow me, and I will make you fishers of men.": Jesus still calls them fishermen, only now, He elevates this title to a far higher, more noble position. He is asking them to lay aside their fishing nets, and to start spreading the net of the gospel (or good news).
3) "And they straightway left their nets, and followed him." Jesus doesn't call all of us to serve Him the same way, some He does ask to go into full time service for Him, but for others, He wants us to serve Him right where we are. The important point in this, we must be obedient to His calling, whatever it might be, to be willing to "straightway leave our nets and follow Him".
"How beautiful on the mountains are the feet of him that brings good tidings, that publishes peace; that brings good tidings of good, that publishes salvation..." Isaiah 52:7