Damian Kyle has been going through Matthew for a while, and I have learned a lot from this series. Here he is specifically looking at the calling of Levi/Matthew the tax collector and makes interesting points both about historical Roman tax collection and the text that were new to me. He points out that Matthew uses "hypocrite" more than any other Gospel, and that as a tax collector Matthew would have known more about hypocrisy than most. In this text, Jesus is relentlessly loving and pursuing sinners who have shunned from Jewish society and it's a reminder for us to do the same (particularly for those who have been expelled due to church discipline over sin issues).
There is also discussion of the impossibility of building a Christian subculture that hides from the world. The false separation touted by the Pharisees was really an expression of weakness. Their Gospel-less religion ultimately wasn't strong enough to come into contact with the world.
Enjoy (on iTunes, you can subscribe to the RSS at the link above).