The king was so angry because he felt he was doing good to invite the people to come for the wedding banquit which they refuesd, upon that they grabbed his servants, treated them shamefully and killed them.

With this parable, Jesus points to the fact that he came to save us, prepered everthing for us but we refuse to listen to him. He suffered for us, yet the Jews crucified him. He has invited all of us to do the will of God, keep to the commendments. But unfortunately, not all of us keep to this. At the last day, only those who did the will of the Father shall inherit heaven.