It was a wonder of Christ's grace, that he would call a publican [the lowest of the tax collector] to be his disciple and follower. It was a wonder of his grace, that the call was made so effectual. It was a wonder of his grace, that he came to call sinners to repentance, and to assure them of pardon. It was a wonder of his grace, that he so patiently bore the contradiction of sinners against himself and his disciples. It was a wonder of his grace, that he fixed the services of his disciples according to their strength and standing. The Lord trains up his people gradually for the trials allotted them; we should copy his example in dealing with the weak in faith, or the tempted believer.
[Excerpt from Matthew Henry's Concise Commentary]
After this, he [Jesus] taught again by the lake shore. As he walked by, he saw a tribal tax collector sitting at his tax booth.
Tribal tax collectors were often tribal members who were given the right to collect taxes for the People of Iron. They could force their own people, under the threat of violence, to pay them. To make a living they would take more than the People of Iron required. But many of them became greedy and took even more than they were permitted. They were hated and looked down on by the people.
The name of this tribal tax collector was He Brings Together (Levi, later known as Matthew). Creator Sets Free (Jesus) went to him and said, "Come, walk the road with me." He got up from his booth, left it all behind, and began to walk the road with him.
Luke 5:27-28 FNV