Read Matthew 9:9-13
Many in the world make judgments in regard to others by observing what company the individual might keep. Who the person spends time with and interacts with is viewed as determining the type of person the individual might be. You could say that it is assumed if you hang out with people who have certain behavior traits, you clearly have the same behavior traits.
This is definitely the rule of thumb which the Pharisees apply toward Jesus. Since Jesus is hanging around tax collectors and sinners, he must be a traitor to the Jews and participate in all sorts of activities which stand in opposition to God. How far from accurate are their assumptions.
Jesus, as always, takes on the challenge presented by the Pharisees in a direct manner. He indicates that the ones who have the greatest need for healing is his focus. The people with whom he is spending time are the ones who need him the most. They are acknowledging that need by coming to him, seeking mercy and to learn from him. Those who view themselves as not having a need for mercy and what Jesus can teach them, do not come.
Reviewing this interaction between Jesus, tax collectors, sinners and the Pharisees demonstrates for us which group each of us may be a member. Are you in need of mercy and teaching from the Lord? Or do you not have a need for such things? Are you sick and in need of the Great Physician? If you are, then seek out and spend time with the Lord, bring others with similar needs to the Lord with you. Jesus intends to hang out with those who recognize their need for him. We would be wise to do the same.