Today's gospel seems harsh. The servants go out into the highways and biways and invite everyone to the feast, then a guest is ejected for not being properly dressed. Two points can be missed.
Firstly, according to the custom of the time, all he would have had to do is ask and the head waiter would have lent him the proper attire.
Second, he is ejected not for his dress, but for assuming that the rules didn't apply to him.
How often in our modern culture do we see people who will be extremely offended if they think they are being disrespected, but in the name of "freedom of expression" feel they have the right to be disrespectful, of others?
From the very beginning of creation God created human beings to live in society, to be one human family. Society requires mutual respect, and mutual respect requires boundaries, limits on ones freedom to act. I may become angry at something you say, but I am not free to smack you in the mouth. And if I choose to violate that boundary, I should expect a commensurate punishment.
Human freedom is never unlimited. From the beginning, God established laws to define those limits, and every unit of society has limits from the natural law that applies to all humans down though the smaller units: nation, state, city, family, and even person to person friendship. All define the boundaries of proper and improper behavior.
In the same way that some are uncomfortable with this parable, some are uncomfortable with the fact that the Church has rules. We as a Church are in fact modeling ourselves on this parable by sending a two-fold message:
1) All are welcome. All are invited to the banquet.
2) In order to share in the banquet, there are certain expectations. As James reminds us, "Faith without works is dead."
One of the biggest mistakes some Christians make is believing that unconditional love means life without boundaries. Watching your alcoholic friend get drunk over and over and saying nothing is not unconditional love, it is cowardice. If we love someone, sometimes the most loving thing we can do is make the boundaries absolutely clear, as well as the consequences for violation of the boundaries.
Imagine what it would be like to drive on roads without lines, signs or stop lights. How unnerved are we when we come to an interesection and the lights aren't working? We feel the stress. Why? Because whether we like to acknowledge it or not. God made us to live in community, and living in community means living by rules.