From: Matthew 22:1-14
The Parable of the Marriage Feast
 And again Jesus spoke to them in parables, saying,  "The kingdom of heaven may be compared to a king who gave a marriage feast for his son,  and sent his servants to call those who were invited to the marriage feast; but they would not come.  Again he sent other servants, saying, 'Tell those who are invited, Behold, I have made ready my dinner, my oxen and my fat calves are killed, and everything is ready; come to the marriage feast.'  But they made light of it and went off, one to his farm, another to his business,  while the rest seized his servants, treated them shamefully, and killed them.  The king was angry, and he sent his troops and destroyed those murderers and burned their city.  Then he said to his servants, "The wedding is ready, but those invited were not worthy.  Go therefore to the thoroughfares, and invite to the marriage feast as many as you find.'  And those servants went out into the streets and gathered all whom they found, both bad and good; so the wedding hall was filled with guests.
 "But when the king came in to look at the guests, he saw there a man who had no wedding garment;  and he said to him, 'Friend, how did you get in here without a wedding garment?' And he was speechless.  Then the king said to the attendants, 'Bind him hand and foot, and cast him into the outer darkness; there men will weep and gnash their teeth.'  For many are called, but few are chosen."
1-14. In this parable Jesus reveals how intensely God the Father desires the salvation of all men--the banquet is the Kingdom of heaven--and the mysterious malice that lies in willingly rejecting the invitation to attend, a malice so vicious that it merits eternal punishment. No human arguments make any sense that go against God's call to conversion and acceptance of faith and its consequences.
The Fathers see in the first invitees the Jewish people: in salvation history God addresses himself first to the Israelites and then to all the Gentiles (Acts 13:46).
Indifference and hostility cause the Israelites to reject God's loving call and therefore to suffer condemnation. But the Gentiles also need to respond faithfully to the call they have received; otherwise they will suffer the fate of being cast "into outer darkness".
"The marriage", says St Gregory the Great ("In Evangelia Homiliae", 36) "is the wedding of Christ and his Church, and the garment is the virtue of charity: a person who goes into the feast without a wedding garment is someone who believes in the Church but does not have charity."
The wedding garment signifies the dispositions a person needs for entering the Kingdom of heaven. Even though he belongs to the Church, if he does not have these dispositions he will be condemned on the day when God judges all mankind. These dispositions essentially mean responding to grace.
13. The Second Vatican Council reminds us of the doctrine of the "last things", one aspect of which is covered in this verse. Referring to the eschatological dimension of the Church, the Council recalls our Lord's warning about being on the watch against the wiles of the devil, in order to resist in the evil day (cf. Eph 6:13). "Since we know neither the day nor the hour, we should follow the advice of the Lord and watch constantly so that, when the single course of our earthly life is completed (cf. Heb 9:27), we may merit to enter with him into the marriage feast and be numbered among the blessed (cf. Mt 25:31-46) and not, like the wicked and slothful servants (cf. Mt 25:26), be ordered to depart into the eternal fire (cf. Mt 25:41), into the outer darkness where "men will weep and gnash their teeth'" ("Lumen Gentium", 48).
14. These words in no way conflict with God's will that all should be saved (cf. 1 Tim 2:4). In his love for men, Christ patiently seeks the conversion of every single soul, going as far as to die on the cross (cf. Mt 23:37; Lk 15:4-7). St Paul teaches this when he says that Christ loved us and "gave himself up for us, a fragrant offering and sacrifice to God" (Eph 5:2). Each of us can assert with the Apostle that Christ "loved me and gave himself for me" (Gal 2:20). However, God in his infinite wisdom respects man's freedom: man is free to reject grace (cf. Mt 7:13-14).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland.
Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.