"While Jesus was having dinner at Levi's house, many tax collectors and 'sinners' were eating with him and his disciples, for there were many who followed him." NIV translation
What a change we see in Levi as he went from being one of the most selfish of men to opening his home not just to Jesus but to the crowd that was following Him. This is an example of someone who has truly came to the Lord and is a sharp contrast to many we see today. Levi's greedy old self was replaced by generosity and hospitality and it did not take a long time but was, in fact, an immediate change of attitude and a sign of genuine repentance.
"When the teachers of the law who were Pharisees saw him eating with the 'sinners' and tax collectors, they asked his disciples: 'Why does he eat with tax collectors and "sinners"?' On hearing this, Jesus said to them, 'It is not the healthy who need a doctor, but the sick. I have not come to call the righteous, but sinners.'" NIV translation
Not only did Levi feed the people that were following Jesus but there were also religious leaders there. Although they were probably not eating, these leaders were welcomed into Levi's home.
These men would have hated Levi and looked down on him because of his job but still they were allowed in and they spoke with Jesus' disciples.
These cowards did not have the courage to ask Jesus the question but instead went behind His back to ask His disciples why He was hanging out with "sinners". We should note that, if we are following Jesus, there will be cowardly gossips who talk about us behind our backs because they do not have the courage to face the Word of God.
Jesus heard about their question and gave a simple answer about His purpose on this earth. Just like the physically sick go to a doctor to be healed, He is the spiritual doctor and He has come to heal those who acknowledge that they are spiritually sick. When He says that He did not come to call the righteous, does that mean that He did not come for all men? No, it simply means that no man is righteous without Him even though these leaders were so full of themselves and their piety.
"Now John's disciples and the Pharisees were fasting. Some people came and asked Jesus, 'How is it that John's disciples and the disciples of the Pharisees are fasting, but yours are not?' Jesus answered, 'How can the guests of the bridegroom fast while he is with them? They cannot, so long as they have him with them. But the time will come when the bridegroom will be taken away from them, and on that day they will fast.'" NIV translation
The religious people still did not understand that Jesus was more concerned with spiritual things than the physical such as fasting. Jesus explained in terms that they could understand. A wedding party is happy and it would be an insult to the groom to show up to the celebration with an attitude of mourning. He goes on to explain to them the fact that He (the Groom) would not always be with them and, at that time, His disciples would fast. In this, He was already preparing them for His crucifixion but they did not realize it.