In Matthew chapter 9:9-13 we read,
"Passing along, Jesus saw a man at his work collecting taxes. His name was Matthew. Jesus said, “Come along with me.” Matthew stood up and followed him. Later when Jesus was eating supper at Matthew’s house with his close followers, a lot of disreputable characters came and joined them. When the Pharisees saw him keeping this kind of company, they had a fit, and lit into Jesus’ followers. “What kind of example is this from your Teacher, acting cozy with crooks and riffraff?” Jesus, overhearing, shot back, “Who needs a doctor: the healthy or the sick? Go figure out what this Scripture means: ‘I’m after mercy, not religion.’ I’m here to invite outsiders, not coddle insiders.” (MSG)
A physician (what we call a doctor) is defined as a professional who practices medicine, who is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury, and other physical and mental impairments.
In order for a person to be truly healthy, there is an important word in the above definition that is missing. Something that our healthcare professionals can't diagnose or recommend a medicine for.
The word that is missing is "spiritual".
Jesus (who is also called "the great Physician") is what I would call a "spiritual" doctor. I want to focus on the word spiritual because even though Jesus did heal physical ailments (as seen in the beginning of chapter 9), his primary focus was on the renewal & restoration of a person's heart, which effects their behavior and their relationship/identity with God.
In Matthew 9:9-13, we see several examples of this.
First we have Matthew who is noted as being a tax collector. This doesn't mean he was like a modern day IRS agent. Matthew was a Jew who was working (probably forcefully) for the Roman government as a tax collector. The Romans were oppressive to the Jews and taxed them heavily. Not only that, but tax collectors had a reputation for being despised as traitors by who were also dishonest in the taxes they got from the people to increase their own wealth. We get another picture of this in Luke 19 (The story of Zacchaeus).
With that context, we can see why the Pharisees (religious leaders) were so upset that Jesus was befriending Matthew.
Before we get too far, I would like to point out that Scripture doesn't tell us that Matthew was a dishonest tax collector. The Pharisees might have been judging him by his occupation alone. If Matthew was indeed dishonest, I would suggest that Matthew would have been suffering from a spiritual impairment caused by greed, circumstance, a hard heart (from being despised by his own people, the Jews) or for some other reason.
Next example. Disreputable characters.
Jesus was well known for being in the presence of drunks, prostitutes, etc. Little girls don't grow up dreaming of being prostitutes. Little boys don't dream of drinking themselves into numbness. Most likely they found themselves in these lifestyle choices by circumstance. How that affects who they are (and what the religious leaders are obviously judging them by) affects their spiritual identity.
Finally, the Pharisees.
Unlike Matthew, Scripture tells us the religious leaders in Jesus' time were suffering from a spiritual aliment. Their actions speak to a spiritual condition. Israel (Jews) were called by God to be honest and compassionate towards others. To be representatives of God to the rest of the world. They were not walking in who God had called them to be and instead were separating themselves from other people who they believed they were better than. This is a heart (spiritual) problem. Jesus says about the Pharisees (in Mt 23:27,28)
"You’re hopeless, you religion scholars and Pharisees! Frauds! You’re like manicured grave plots, grass clipped and the flowers bright, but six feet down it’s all rotting bones and worm-eaten flesh. People look at you and think you’re saints, but beneath the skin you’re total frauds."
The truth is that we are all spiritually ill in some way. Not one of us is better than another. We may suffer from different symptoms of spiritual sickness that has it's roots in thousands of different circumstances, but we are all in need of the great Physician. This is what separates Matthew and the "disreputable characters" from the Pharisees. Jesus called and Matthew followed. The drunks, prostitutes, etc sought Jesus out. In comparison, Jesus spoke to the religious leaders and they hardened their hearts and desired to kill him (which again is a spiritual condition).
It's a great example for you and me. Do I seek after Jesus? When Jesus calls, do I follow and allow him to diagnosis and treat my spiritual impairments, or do I dive further into sickness and harden my heart?