“And the scribes of the Pharisees, when they saw that he was eating with sinners and tax collectors, said to his disciples, ‘Why does he eat with tax collectors and sinners?’”
 
—Mark 2:16
 
Why did Jesus go to parties with sinners and tax collectors?  Why did He do it?  That's the question the Pharisees asked; and maybe we need to answer that question from the words of Jesus.  Why did Jesus befriend the sinners?
 
Because people are sick and hurting, and they need a physician.  Jesus did not see these tax collectors and sinners as pagans.  He saw them as patients who needed a physician.  He saw them as broken people who needed someone to heal their broken lives. 
 
Sin is much like a disease, just a little germ that enters the body and attacks the immune system.  Then that germ begins to spread throughout the body.  Having spread throughout the body, then the body is sapped of its energy and of its strength.  And if not cured, the disease can kill.
 
That is why it's so important to know Jesus. He is the only one who is the cure for mankind's ills.  But there's only one Great Physician; and I beg you, church, that we be friends of the wounded heart as well.  People are desperately sick and in need of the Great Physician.
 
Sometimes we have the idea that we want to protect ourselves from the sickness so much that we've isolated ourselves from those who don't know Christ.  We want to be strong against sin. Please, Christians, let's don't get the idea that we ought to be so offended by sin that we don't love people who are sinners.

Jesus went to parties with sinners, so that people could come home and have a party with Him.