The man spoken of in the Gospel came to the wedding feast and was cast by the king’s command into exterior darkness because he had not on a wedding garment.
That is because he had not “put on the new man who according to God is created in justice and holiness of truth”, and for not having put away lying and those feelings of anger against his neighbor which he cherished in his heart (Epistle).
Thus will almighty God treat all those who, while belonging to the body of the Church by their faith, are found within the wedding-chamber without being clothed with the robe of charity. Since they are not animated by sanctifying grace, they have no share in the soul of the mystical body of Christ. “Wherefore,” says St. Paul, “putting away lying, speak the truth every one with his neighbor, for we are members one of another… Let not the sun go down upon your anger” (Epistle). Those who do not fulfill this command will be cast by the supreme judge into the torments of hell, like those who refused the invitation to the wedding feast of the king’s son, that is of Jesus Christ with His bride the Church, and who slew the prophets and apostles who were sent to bear the invitation.
The wedding guests were replaced by those whom the king’s servants found in the highways; the Jews by the Gentiles. To these last, at Pentecost, the apostles turned, filled with the Holy Ghost. And at the last Judgment, foretold on these last Sundays of the cycle, these rewards and punishments will be final. The elect will take part in the eternal marriage feast, while the damned will be cast into exterior darkness, into the avenging flames, where there will be weeping and gnashing of teeth.”
Source: Dom Gaspar Lefebvre, OSB, 1945, adapted and abridged.