The wedding garment
What the garment is that the guest lacks, and how the parable's judgment relates to election.
Matthew 22:1-14
1Jesus answered and spoke to them again in parables, saying,
2“The Kingdom of Heaven is like a certain king, who made a wedding feast for his son,
3and sent out his servants to call those who were invited to the wedding feast, but they would not come.
4Again he sent out other servants, saying, ‘Tell those who are invited, “Behold, I have prepared my dinner. My cattle and my fatlings are killed, and all things are ready. Come to the wedding feast!” ’
5But they made light of it, and went their ways, one to his own farm, another to his merchandise,
6and the rest grabbed his servants, and treated them shamefully, and killed them.
7When the king heard that, he was angry, and sent his armies, destroyed those murderers, and burned their city.
8“Then he said to his servants, ‘The wedding is ready, but those who were invited weren’t worthy.
9Go therefore to the intersections of the highways, and as many as you may find, invite to the wedding feast.’
10Those servants went out into the highways, and gathered together as many as they found, both bad and good. The wedding was filled with guests.
11But when the king came in to see the guests, he saw there a man who didn’t have on wedding clothing,
12and he said to him, ‘Friend, how did you come in here not wearing wedding clothing?’ He was speechless.
13Then the king said to the servants, ‘Bind him hand and foot, take him away, and throw him into the outer darkness. That is where the weeping and grinding of teeth will be.’
14For many are called, but few chosen.”
What each tradition says
Rabbinic / Midrashic
It refers only to mitzvot, good deeds, and Torah. Rabbi Yehuda HaNasi compared this to a king who invited guests to a feast and told them to bathe, anoint themselves, press and launder their garments, and prepare themselves.
Kohelet Rabbah, Kohelet Rabbah 9:8 — The Sefaria Midrash Rabbah, 2022 (served by Sefaria API) — Parable of the king's feast (on Ecclesiastes 9:8)
Patristic
Irenaeus states that it was made manifest that after our calling we ought to be adorned with works of righteousness, so that the Spirit of God may rest upon us. This, he says, is the wedding garment, of which the apostle speaks: "Not for that we would be unclothed, but clothed upon, that mortality might be swallowed up by immortality."
Irenaeus, Against Heresies, Book IV (Ante-Nicene Fathers, Vol. 1) — Book IV, ch. 36, §6
Catholic
Haydock says the guest without a wedding garment represents every sinner void of God's grace. To enter with unclean garments is to depart this life in the guilt of sin. So the missing garment points to lacking God's grace, and unclean garments point to dying in sin.
George Leo Haydock, George Haydock's Catholic Bible Commentary (1859) — On Matthew 22:12
Orthodox
Chrysostom says the garment is life and practice. The calling and cleansing are of grace, but once called and clothed in clean garments, continuing to keep them is the diligence of those called. This is why He takes a strict account.
John Chrysostom, Homilies on the Gospel of Saint Matthew (Nicene and Post-Nicene Fathers, First Series, Vol. 10) — Homily LXIX, on Matthew 22:1-14
Reformed / Protestant
The debate over whether the wedding garment is faith or a holy life is useless, since faith cannot be separated from good works, nor good works from faith. Christ means the Lord calls us on the condition of being renewed by the Spirit, putting off the old man and leading a new life, so the garment corresponds to our calling.
John Calvin, Commentary on Matthew, Mark, Luke — Volume 2 (Calvin Translation Society) — On Matthew 22:11-14
Evangelical
Wesley says the wedding garment is the righteousness of Christ, first imputed, then implanted. He notes this has no relation to the Lord’s Supper, but to God’s proceeding at the last day.
John Wesley, Wesley's Notes on the Bible (Notes on the Gospel According to St Matthew) — Note on Matthew 22:12