I don't understand what's being said in Matthew 8:11-12. Are the many who come from east and west like the centurion -- those with great faith -- while the subjects are the Pharisees, or those who appear to have high positions here on earth but in the kingdom will thrown outside because of their lack of faith?

The outsiders are the Gentiles; the insiders, the Jews. This is a major theme in Matthew's gospel. I think you've got it!