Tarshish

Nope, this isn't about Jonah. This is about trading ships. It seems throughout Hebrew Scripture that ships were originally referred to as "ships that could go to Tarshish." It makes more sense to us to say "trading ships."

But that's not the point either.

In both Samuel–Kings and Chronicles–Ezra–Nehemiah, the text recounts that Jehoshaphat built a fleet of trading ships but they were wrecked before they set sail. A prophet noted that this was because he had made the ship-building alliance with Ahaziah king of Israel "who was guilty of wickedness."

It makes sense that God wouldn't be keen on an evil king. More sense that he would prefer a good king to not ally himself with an evil king. But I think the point may be one step deeper.

Jehoshaphat oversaw one of the most amazing military victories ever. Judah defeated three nations by trusting in YHWH and singing his praises. They crested the hill overlooking the battlefield, and God had already made the nations destroy one another. The only remaining task was to fetch the plunder. Again, this was all about trust in God, and he blessed Judah for it.

Now a nation must be prosperous to afford a fleet of ships. And God was indeed prospering Judah. But Jehoshaphat did not trust YHWH to provide the ships; he signed a contract with someone who had explicitly turned away from YHWH. That's a good reason to wreck the ships.

A final detail is that this was an apparent imitation of Solomon. Solomon was so enormously prosperous that his fleet of ships anchored in the same harbor generations before Jehoshaphat's wasn't really necessary, but God blessed Israel with it. In effect, Jehoshaphat was trying to say that he was as great as Solomon. Only it was YHWH who made Solomon great, and anyone who tries to measure up to that sort of greatness by allying with an enemy of YHWH is doomed to fail.