What does Matthew 22:8 mean?

The time has come, in Jesus' parable, to celebrate the wedding of the king's son (Matthew 22:1–7). The oxen and calves have been slaughtered. The feast is prepared. The king, though, has no guests. The original guests he invited to the wedding refused to come, to the point of murdering the king's messengers. The king now describes those originally invited guests as "unworthy." This is meant as a parallel to how Israel's leaders rejected God's prophets and were subject to judgment.

Religious Jews of that era understood the idea of God drawing clear distinctions around what could be in His presence. Under the Old Testament law, that even extended to excluding certain people from aspects of worship. This included those who disobeyed God's law, but also meant those with various health issues. Some in the Jewish ruling class prided themselves on their spiritual worthiness before God and their ability to keep the law and extra rules more than others.

Especially in context with the prior parables (Matthew 21:28, 33), it's becoming clear that Jesus meant to represent Israel's religious leaders with the guests who refused to come to the king's feast. Those listening must have been shocked by the claim made in this verse. The king calls those very people "unworthy," with their favored status revoked due to their own refusal to honor the king's son.