The King is Elohim (Psalm 45:10-16). The Wedding Feast is the marriage supper of the Lamb. This is the event that will apparently usher in the Kingdom of Heaven. His slaves are His prophets He sent to warn Israel (Jer. 25:4). Those who had been unwilling to come are the Jewish people who would not listen to Him in that day, especially the religious leaders (Jer. 6:16-17).
When the Pharisees heard that Yeshua was casting out demons, the claimed He was doing this by the power of Beelzebub. Now the Pharisees want a sign “from heaven.” They wrongly reasoned that some miracles here on earth could come from Beelzebub. They thought that if they saw a sign from heaven, then they could determine if Yeshua is really a prophet from Elohim or not. Yeshua showed signs before, why would He not show a sign for the Pharisees? Yeshua did not want them to heed His warnings. He already said they were not to understand His message and that is why He spoke in parables (Matt. 13:9-15).