Earlier in this parable Jesus had told of a king who invited guests to the wedding of his son. But they had all refused repeatedly; they had beaten and killed the messengers who asked them to come. The king was very angry and sent in the army to deal with them and destroy their comfortable lifestyle. But the king still wanted people to enjoy the wedding and the banquet and so he decided to invite other people who had no reason to expect any invitation from him.
 
More messengers were sent out into the city. They sought out anybody who would respond and told them that they would be welcome in the palace. They did find some decent people, but those they found on the street corners were not morally good. However, they were told that they must come, and that they did not need to worry about their clothes because suitable attire would be provided (Matthew 22:11-12).
 
They did come, and many of them too. The banqueting hall was full. They had all been invited, just as the original guests, but these were willing to say, "Yes". Jesus was talking about the tax collectors and immoral women who were willing to listen to Him and who trusted Him. The original guests were the religiously correct people of Israel, but they were not willing to honour Jesus. They forfeited their place in the palace, because (despite their claim to honour the 'king') they really despised God.
 
Jesus had already said, "Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven." (Matthew 7:21). The 'good' religious leaders refused to do what God wanted, but the bad people in society were willing to trust Jesus. What a lesson to us. It is not our piety or rituals which demonstrate our devotion of Christ, but our obedience in responding to His call. If you have heard Him call - obey! There is no other safe option.