Levi made a great feast for him in his house. There was a great crowd of tax collectors and others who were reclining with them. Their scribes and the Pharisees murmured against his disciples, saying, "Why do you eat and drink with the tax collectors and sinners?"
Jesus answered them, "Those who are healthy have no need for a physician, but those who are sick do. I have not come to call the righteous, but sinners to repentance."
- Luke 5:29-32 (WEB)
As with us today, the Jews recognized eating and drinking together as a form of fellowship. The scribes and Pharisees thought Jesus had lowered His standards by having a good time with a bunch of sinners and tax collectors. But the real reason Jesus was eating with them was lead them to repentance. That was His purpose. Fellowship with them was just a means to that end.
...but then again, godly repentance leads to salvation (2 Corinthians 7:10), and salvation leads to true fellowship with God (1 John 1:1-3). Jesus ate and drank with sinners so that He might eat and drink with them in the kingdom of heaven.