The king decided to open up the feast to everyone. He sent his slaves out on the streets to invite strangers to the wedding feast. This was unheard of! Kings only invited prestigious people to events like this, but this king invited everyone--including evil people (Matt. 22:10). Just imagine all the thieves, murderers, and prostitutes at this feast to honor his son. This shows that God loves everyone and wants every person to be saved, no matter how evil they may be.
In those days when a wedding was held, the host bought a wedding garment for each person to wear. It was a free gift to the invited guests. All the person had to do was put it on, which showed honor and respect for the person being married. This man had no excuse because he refused the free gift from the king. The interpretation is the wedding garment was "the robe of righteousness" (61:10). He was at the feast just to get the free food and had no interest in honoring the son. Many people today want to go to heaven to get the free food, but have no interest in living for the Lord. On Judgment Day, they will be like the man who refused to wear the wedding garment.