Matthew was chosen to be the inspired author of the longest record we have of the life of Christ, yet he says little about himself. Almost everything we know about him--from the Scriptures at least--is found in this one verse.
As a publican, or tax collector, he would normally be greatly disliked by other Jews (note Matthew 9:11), yet Jesus chose him as a disciple. Matthew responded immediately to what seemed almost an off-handed invitation from Jesus, and his whole subsequent life was changed.
Matthew reports a similar response by Peter and Andrew. When Christ told them to follow Him, "they straightway left their nets, and followed him." Similarly, when He called James and John, "they immediately left the ship and their father, and followed him" (Matthew 4:20, 22).
But there is more to this than meets the eye. John and Andrew had first been disciples of John the Baptist, who had directed them to follow Jesus (John 1:35-37, 40). Probably this was true of the rest of the disciples too. When the eleven had to select a man to take the place of Judas, the criterion was that he must be one who had "companied with us all the time. . . . Beginning from the baptism of John" (Acts 1:21-22).
Evidently all the disciples had been baptized and prepared by John, who had himself been called "to make ready a people prepared for the Lord" (Luke 1:17). Matthew’s remarkable call, like that of the others, must have been preceded by an unrecorded history of his own personal repentance and faith. He must have come to John as one of the "publicans to be baptized" (Luke 3:12) and thereby been gladly ready to go when Christ called him. HMM http://www.icr.org/articles/type/6/