To fund this empire, each province was responsible for collecting taxes and remitting them to Rome. Tax collecting was contracted out via auction to local individuals (or groups) in each province called Publicani.
Publicani bid for the right to collect taxes and were required to pay the State in advance of the actual collection. This position was highly sought after because the collectors could keep anything in excess of what they bid. This created a system filled with corruption and allowed, even encouraged, the exploitation of (mostly-illiterate) citizens.
The average working-class Jew in those days could expect to have 60-70% of his annual income consumed by tithes, taxes, and mandatory fees imposed by the Roman Empire and Temple priests.
Many tax collectors in the region of Judea (located approximately in the area we currently know as the West Bank of Israel, covering parts of four Roman provinces) became extremely rich by over-charging people more than Roman law required. Further, the tax collectors would even loan money (at 4% per month for Jews, higher for non-Jews) to those unable to pay the illegal taxes. Those who were unable to pay their debts would eventually find themselves (and even family members) sold into slavery to close out their accounts.
Because of this, tax collectors were some of the most hated and vilified members of society. In Judeah, most people viewed them as the worst of the worst, especially as many of them abused their power and cheated fellow Jews of their livelihood.
Jesus selected Matthew, a rich (and greatly feared) tax collector as one of the twelve original apostles. Matthew immediately abandoned a life of luxury and high privilege to become a lowly Apostle upon being called to serve by Jesus.
Matthew subsequently went on to become one of the four Evangelists during early Christianity. He authored his own book in the New Testament (thirty years after Christ's death, in about 60AD) which is considered to be the most systematic and detail-driven book of the four Gospels -- likely a result of his previous profession.
That being a follower of Jesus could transform such a hated individual into one of the most important figures in Christianity speaks strongly to the redemptive power of Jesus upon the lives of anyone who chooses his way.
