But this is first a parable of grace. Of a king who invites his desired guests a second time, who gives them the benefit of the doubt for perhaps having misunderstood the first invitation. It tells of the graciousness of a king who invites undeserving people to his banquet, and is delighted to have them present. Good or bad, he invites them, and they respond with appreciation at the honor. This is a parable of grace.
Judgment comes only when grace is spurned.
It is also a parable of the servants' present duty to spread wide the king's gracious invitation to any and all. That's what we're called to do. Never mind that some people are too busy, or too rude, or abusive to the king's servants. Our King knew rejection, and we bear just a bit of the rejection that is directed at Him. We are to go out to whosoever will respond and come.