"Go ye therefore into the highways, and as many as ye shall find, bid to the marriage.
So those servants went out into the highways, and gathered together all as many as they found, both bad and good: and the wedding was furnished with guests." Matt 22:9-10
great question. I also wonder about the city from God (in the book of the revelation) as well, with regard to those outside the gate and not permitted in (where there is weeping and gnashing of teeth.) Some would say that this refers to Hell (outside the gates) but a literal interpretation of this sort puts God's Holy city in the midst of Hell.
Personally, I think a spiritual meaning is most significant, but in the Old Testament scriptures the term "outer darkness" was used to describe what was outside the camp of Israel while traveling through the wilderness. People who became ritually unclean would sometimes have to move temporarily outside the camp, until they could be declared clean again by a priest. Consequently the passage may refer to the millennial kingdom in part in a literal way. Since scripture says that there will be births (infants at least) and deaths in the millennial kingdom, and a remnant of the nations as well as a restoration of Israel, there must be survivors that are compelled to become part of the kingdom as the kingdom of Christ will extend everywhere.
I can't imagine a person being unhappy with that, but the scripture indicates punishment for sin and rebellion as a promise during the millennial reign. The unclean may not enter the Holy City but remain under the authority of the king.
I think that in Jesus' parable, from Matthew chapter 22, the more significant point is found in the wedding garments themselves. What does the wedding garment represent? I see garments in scripture, starting in the book of Genesis, as representing a covering for sin. According to scripture, the only effective and permanent cover for our sin is the righteousness of God imputed to us for our faith in Christ. I'm inclined to believe that the wedding garments represent a faith in the wedding (they come prepared for a wedding just as we are to be prepared for Christ's return.) Whatever the specifics might be, the contrast was with those who were invited, and for nearly 2000 years, those that were invited and declined, have been harassed and pursued, slandered, forced into ghettos, rounded up and murdered, despised by all. So, I suppose the question to ask is "do we all have on our wedding garments?"