Thank you Mark Dever, in The Message of the Old Testament for this that I’ve never seen before:
“It is also interesting to note that Jonah spent the same amount of time in Nineveh that he did in the fish – three days. By saving a city in the same amount of time that Jonah spent in the belly of a fish, was God teaching Jonah how many opportunities are wasted when his people flee from him? And was he subtly reminding Jonah of his own grace to him?”
Another one of those observations that are obvious once someone’s shown you.