The "wicked and wild wind" (forces of evil) broke down the barriers before this king, allowing the darkness within him to break forth, and chaos to ensue. The king was changed, and not for the better. Something dangerous stirred inside him and channeled all that had been good in his life into something evil.

These lines refer to Lot's wife being turned into a pillar of salt for looking back at Sodom as it was destroyed (Genesis 19), and to the Parable of the Wise and the Foolish Builders (Matthew 7, Luke 6), where the wise man built his house upon a rock (God) and the foolish man built his house upon the sand (take one guess at whose house collapsed in the flood). This king built his kingdom on his own power and strength and wealth, instead of on a firm foundation. He also couldn't help but turn back to his sinful ways (and a king's doings influence greatly what is considered acceptable in his kingdom, so his sin could have led to sin by his subjects). It took his fall from power to make him realize that he had wasted so much time building beautiful things (castles take a very long time to build, and are beautiful each in there own way) on a weak foundation. Just as salt and sand are hardly considered sturdy materials to build upon, neither are human frailty and sin. Now the king reflects, in this song, how his fall made him realize, or discover, that he had built everything on weakness instead of strength, and warns the listener against doing the same.

We aren't told whether the "honest words" that are so absent in his life are from his mouth or from those around him, but it is obvious that in either case with the leaving of the "you" mentioned (whether the you is an adviser (think Merlin), a general or officer, a savior (think Jesus), or a queen/girl), when they left, the king either had no reason to be honest to those around him, or changed enough that his advisers and officials had no reason to be honest to him. Both of these possibilities would negatively impact a king, and could easily result in his downfall.

Lot's wife was turned to a pillar of salt (Genesis 19), when she turned back and looked at the city of Sodom as it was destroyed. One of Jesus' more popular parables (Matthew 7, Luke 6) is about the fool who built his house upon the sand. Combine these two things, and it's easy to see that the parallelism here. This king thought that the world was his, and he built his kingdom upon his own strength and wealth, instead of building on a firm foundation. If this wasn't enough, he turned back to his sinful ways. As we know, neither salt nor sand make for firm foundations, and neither do sin and human frailty. When this king fell from power, he realized all his mistakes, how the foundation he built upon was weak, he regrets the time he wasted (castles take a long time to build) and wishes he could restore everything to its previous splendor (castles are also beautiful, in their own fashion). When his world crumbled, and all that he built fell to the ground, then he repented of his ways. His words are a warning to the listener; don't make my mistakes, before you build your beautiful towers on a foundation that can't stand.