Micah to Jonah
Sins and Jonah cast into the sea.
Mercy In The Seas
Micah's last paragraph is heavy on the theme of mercy. Arguably, the mercy God shows to Nineveh in the book of Jonah is the foremost example in scripture.
Micah also deals with "tossing into the seas," which is practically Jonah's brand.
Three Clues
There's more going on in Micah's lead-in to Jonah then a simple nod to the basic theme of mercy and tossing sins into the seas. Micah provides three important clues about the identity of Jonah's Nineveh that ultimately explains why God would send a prophet their way to extend mercy to them.
The first clue Micah gives to identify Nineveh is the way Micah says God is going to show mercy to a "remnant" of "Jacob." That's odd. God shows mercy to Nineveh in the next book, not Israel. Or does he?
The Book Chain assumes Nineveh is a part of Jacob. How could this be? Easy. Israel was hauled to Nineveh by the Assyrians. By the time Jonah gets to Nineveh the Israelites are assimilated. God deals with "Nineveh," not "Israel," because the Israelites that had settled in Nineveh are mostly indistinguishable from Ninevites by this time, and likely taking over leadership in Nineveh.
The second clue Micah gives to establish Nineveh's identity is the reference to God casting all our sins into the seas. In Jonah what goes into the sea is the prophet. How do these relate?
Jonah is thrown into the seas as a parable. His audience had been cast into the sea. "Seas" represent "nations." Israel was tossed into the seas when they were forcibly taken to Nineveh. So Jonah goes for a dip on his way to Nineveh to illustrate what had happened to his audience.
To be sure, Israel's sins were cast into the seas, it's just that the Israelites went into the seas with them. It might have worked differently if they had been willing to part with their sins.
The third clue Micah gives about Nineveh's identity is the reference to God's sworn promises to Abraham. Here's one of those promises.
Verse 17 says God swore that Abraham's descendants would inherit the lands of their enemies. How would they do that? Is there a story in the Bible where Israel did this? They took the Promised Land from the Canaanites. Does the promise end there? Clearly the scope is much wider, it mentions all nations being blessed by Abraham's descendants. How about Assyria? Sure, Assyria is inside the scope of "all nations" and they were a brutal "enemy" of Israel.
Ultimately the fulfillment of the promises to Abraham by scattering Jacob into the nations of the world sets up the great commission given by Jesus later and explains why Jesus could say things like you won't finish going through the cities of Israel before I come again. It's clear too, from the book of Jacob, late in the New Testament, that the tribes of Israel are still in the nations of the world, but that God has not forgotten them or lost track of their identity even if they have forgotten who they are.
Jonah is just one chapter in the Bible's story of how the tribes went into the world. Micah prepares his readers to not miss what was really happening when God sent a prophet to Nineveh.