Levi, or Matthew, worked for the Roman government as a Tax Collector. Tax Collectors were despised because they not only worked for Rome, but they were notorious for overtaxing people and keeping the excess for themselves. Jesus was criticized for eating with "tax collectors and sinners."
Matthew worked for "Big Government Rome." Simon the Zealot, another one of Jesus' Disciples, would have been known as a revolutionary who opposed Rome and wanted a smaller Israeli government. Jesus had room for both extreme political views in His Disciples.
Disciples are people who are called to follow Jesus. Levi (Matthew) answered the Call and left everything to follow Jesus. Jesus Calls us to follow Him too. How do we answer the Call? Do we leave everything behind and let Jesus lead or do we try to limit our response and only follow Jesus when it is convenient? If there is room among Jesus' Disciples for a Tax Collector like Levi (Matthew), there is also room for sinners like you and me! When we answer Jesus' Call to follow Him, He leaves our sins behind on His cross and gives us a new life.