This verse is, of course, part of Jesus ’parable of the wedding feast that describes the relationship between the Christian church and Jesus. Several interpretations have been put forward. It is often thought that Jesus here means "many" are Jewish people but "few" are Gentiles. However, it is important not to draw too direct conclusions.
Pulpit Commentary states:
The rejected guest is a type of a numerous class (see Matthew 20:6).
All the Jews had first been called; then all the Gentiles; many were
they who obeyed not the call; and of those who did come in, many were
not of the inner election, of those, that is, whose life and character
were worthy of the Christian name, showing the graces of faith,
holiness, and love. --
It would not make sense to think that either of these words would only apply to a particular group. It could simply mean that there were many invited from the nation of Israel to become members of Christ’s "bride", that is a christian congregation, but only a few natural Israelites were chosen. Jesus preached primarily to the Jews. It was not until after his resurrection that the message was extended to the Gentiles. It does not also indicate that the majority of those who are actually 'invited' would prove unfaithful and have to be replaced. I think it is clear that there is a simple idea behind the verse; Many hear the message of Christ but quite a few actually accept it.
This was a royal wedding, and it is likely that a special garment was provided by the royal host for his guests on an occasion such as this. If so, the failure of one of the guests to be clothed with the marriage garment indicated that he had spurned the garment provided by the king when it was offered to him.
Just as a uniform or special attire identifies one as belonging to a certain organization or supporting a certain movement, so clothing, as used symbolically in the Bible, indicates the identification of a person by the stand he takes and his activities in harmony with it, as in the case of Jesus’ illustration of the marriage garment.