After healing the paralytic, Jesus is found again on the shore of Galilee teaching the multitudes.
In the same manner that He called the four fisherman to follow Him (cf. Mark 1:16-20), He here called upon "Levi the son of Alphaeus" who was "sitting at the tax office" (Mark 2:14). When considering the parallel accounts of this event, Mark and Luke use the name "Levi" and Matthew uses the name "Matthew" (cf. Matt. 9:9; Luke 5:27,28). Undoubtedly, they all refer to the same individual (a careful look at the details in each context will establish this). The fact that two different names are used to refer to the same person should not be disturbing since many in that day were known by two different names (or their names were changed)--for example, Lebbaeus (Thaddaeus), John (Mark), Simon (Peter), Saul (Paul), Nathanael (Bartholomew), etc.
Matthew responded as the four fisherman had previously. He left everything and followed Jesus (cf. Luke 5:11,28)! He was called to a higher life, a nobler work. He would no longer gather perishable money for the Roman treasury but souls for the kingdom of heaven! Is there a greater work than this?
It should be understood that His obedience to Jesus' words was not performed in ignorance (or as a mindless zombie who could not resist Jesus' call). Matthew was certainly already a disciple, as were the four fisherman when they received their invitation to follow Him. It is good to be reminded that we know very little about Jesus' activities while here on Earth. We do know what we need to (cf. II Tim. 3:16,17), but He did so much more than we have record of (John 21:25). There is no doubt that Matthew and Jesus were already acquainted to some degree.
By calling a tax collector to follow Him, Jesus shows that He didn't subscribe to a stereotype of that day--namely that tax collectors were no good. In that era, to be a tax collector was to be hated by Jews because: (1) the tax collectors worked for the Romans whom the Jews hated, (2) they naturally despised paying taxes, and (3) tax collectors were often dishonest (i.e., they overcharged in order to pad their own pockets! - cf. Luke 3:12,13). The Jewish people considered their fellow countrymen who collected taxes for the Roman government to be traitors and would not associate with them.
For Jesus to show an interest in Matthew is significant indeed. It underscores a truth that is seen repeatedly in the New Testament--God loves all people and desires the faithful obedience of all. Today, Jesus is calling each of us--through the gospel (II Thess. 2:13,14)--to follow Him. Have you answered the call?