This Parable is teaching us something about salvation. When God bids a Sinner come to the wedding of the Lamb to his bride by grace, that Sinner takes the lowest room (hell under a sense of condemnation). There he sits until Christ comes saying "friend, go up higher". This is a picture of Christ assuring the heart of his redeeming grace. The self-righteous on the other hand believe their works merit the highest places (heaven). But when Christ is revealed in all his glory in the Day of Judgment, they shall begin with shame to take the lowest room in hell everlasting. That is what Christ is declaring in this parable.