From The Gospel of Matthew by Curtis Mitch and Edward Sri, commenting on Matthew 22:14:
The final verse captures the message of the parable in a short maxim. Many are invited, Jesus says, but few are chosen. The point is that all are called to the kingdom, but not all will be found worthy to possess it. Some will decline the invitation and so exclude themselves from its blessings; others will accept it but will not follow through in putting its demands into practice. Those found acceptable are those committed to directing their lives by the gospel. They clothe themselves in the garments of true repentance and Christ-like righteousness.