Citation: Matthew 9:9 || Mark 2:13-14 || Luke 5:27-28, the call; the feast and controversy follow in each (Matthew 9:10-13; Mark 2:15-17; Luke 5:29-32).
The narrative
As Jesus passes by, he sees a man sitting at the tax collection booth, Matthew in the First Gospel, Levi in Mark and Luke (Mark adds "son of Alphaeus"). Jesus says, "Follow me." He rises, leaves everything, and follows (Luke's emphasis).
Then a great feast at the tax collector's house: "many tax collectors and sinners" recline with Jesus and his disciples. The Pharisees and their scribes object to the disciples: "Why is it that he eats and drinks with tax collectors and sinners?" Jesus answers: "Those who are healthy have no need for a physician, but those who are sick. I came not to call the righteous, but sinners to repentance." (Mark 2:17; Luke 5:31-32). Matthew's account adds Jesus' charge to learn the meaning of "I desire mercy, and not sacrifice" (Matthew 9:13, quoting Hosea 6:6).
Who Matthew is, and the Levi/Matthew question
A tax collector (telōnēs) gathered Rome's tolls, often by over-charging, and was despised as a collaborator and a ritual outsider. That such a man is summoned directly into the Twelve is the scandal the story turns on.
The traditional identification, held since the early church, is that Matthew and Levi are the same man, one person with two names (compare Simon/Peter, Saul/Paul), and that he is the apostle Matthew to whom early tradition ascribed the First Gospel. A minority of scholars distinguish Levi (a disciple) from the apostle Matthew. The question is noted here; the dominant reading treats them as one.
Theological framing
The tax-collector-becomes-disciple paradigm, grace reaching the most despised insider-outsider; the call is to a man no rabbi would have chosen, and he leaves his lucrative post at a word.
"Physician for the sick", Jesus' mission statement: he comes precisely for those who know they are "sick," not for the self-assured "righteous." Table fellowship with sinners is not compromise but the very shape of his mission.
"Mercy, not sacrifice" (Matthew's addition), the Hosea citation reframes true religion around compassion over ritual correctness, indicting the Pharisees' objection at its root.
Pairs with Zacchaeus, Luke's other great tax-collector encounter (Luke 19:1-10) makes the same point with another rich collector restored.