Matthew describes himself as "Matthew the tax-gatherer" (Matt 10:3). He is the only apostle whose name is associated here with an occupation. Apparently Matthew never forgot what he had been saved from and never lost his sense of awe and unworthiness over Christ's forgiveness. 
 

Matthew 9:1-8, where he sets the scene of his own conversion, tells us Jesus forgave the sins of a paralytic man and then healed him of his paralysis. When the Jewish scribes accused Him of blasphemy for claiming to have the authority to forgive sins, He said to them, "Why are you thinking evil in your hearts? For which is easier, to say, ‘Your sins are forgiven,' or to say, 'Rise, and walk?" He wanted them to know that His miracles testified to His deity. As God, He could as easily forgive sins as He could heal diseases. 

Immediately after that account Matthew gave the account of his own call. It's as if he wanted his own salvation to serve as an illustration of Christ's ability to forgive even the vilest of sinners. Matthew 9:9 says, "As Jesus passed on from there, He saw a man, called Matthew, sitting in the tax office; and He said to him, 'Follow Me!' And he rose, and followed Him." 

When the Pharisees questioned Jesus' practice of associating with tax-gatherers, He said to them, "It is not those who are healthy who need a physician, but those who are ill.... I did not come to call the righteous, but sinners" (w. 12-13). The Pharisees were sick with sin but thought they were healthy. Matthew and his associates knew they were sinners who needed a Savior. 

Do you share Matthew's humility and sense of awe at receiving Christ's precious gift of forgiveness? I pray that you do and that you are continually praising Him for it