What does Matthew 22:12 mean?
In a parable, a king has invited an unlikely collection of people to the wedding feast for his son. They have literally come from the roadways and street corners at the urging of the king's servants. The wedding hall is full of both bad and good people who have all said yes to the king after his first chosen guests said no (Matthew 22:1–11).Now, though, the king has seen a man who is not wearing a wedding garment. The story does not explain whether the man refused to wear a garment provided by the king's servants or whether he simply came unprepared and in unclean clothes, hoping to be included in the feast anyway.
Though the king first addresses the man as friend, what comes next suggests this is a formality. As a parallel to how God interacts with sinners, this reflects how God demonstrates a level of love even to those who hate Him (Matthew 26:47–50).
The king asks how the man was able to get into the wedding hall without a wedding garment. The man has no answer to this. Either the servants failed to screen the guests carefully, or the man snuck into the hall in some way. In any case, the man will not be allowed to stay. His lack of a proper garment means he's not here to fully participate, or to cooperate—he's simply looking to gain benefit on his own terms (Matthew 7:21–23).