In the Book of Jonah, Why Did God Send Jonah to Nineveh?

This is a difficult question because what it forces us to do, is it forces us to think about two different old testament covenants. The first one that we have to ponder is found in Genesis Chapter 12, when God makes covenant with Abraham. Part of that Abrahamic covenant is when God says to Abraham, through you I will bless all nations. Now he does not have in mind there a universal blessing, meaning he's going to save every single person from every single place, under every single place under the sun. What he means is, what we see in the final version the book of Deuteronomy when the prophet or when John comes back and sees, he says behold there's a number that I cannot count. Myriads upon myriads, thousands upon thousands and he says behold they are from every tribe tongue and nation. It's not everyone from every tribe, but it's people from every tribe, every tongue, and every nation. So, the Abrahamic covenant is reminder to us that salvation was never nationalistic, it was never meant to be one national people of God. That the very plan of redemption from the very beginning meant to cross all of these generations all of these tribe, al of these tongues so, that's the first part.

Second part is this, the nation of Israel was under the Mosaic covenant. Here's that second covenant, in the Mosaic covenant he is in relationship covenantally with these people, and where there's covenant, there's law. And where there's law there must be both covenant blessing and covenant cursing. And where the people of God are obedient to the covenant law then God is obligated to shower them with covenant blessing. But where there is covenant cursing, he's now obligated to shower them with covenant curses. 

One of the covenant curses as seen in Deuteronomy Chapter 28, is that if my people are so disobedient and continually transgress my covenant law, I will raise up for them an enemy nation. And that enemy nation will come into my people and they will destroy them, take them captive, and lead them back into captivity. And so what Jonah does is he is now the prophet who is in the first half of his career going to the people of God saying repent, repent, repent and go back to the covenant law, and of course they do not. So, then God is obligated, he's not being upset, he's not being angry, he's obligated now to shower them with the covenant curses. So, he sends his prophet to the Ninevites, and he preaches to them and a few years later it is the nation of Nineveh that rises up in 722 BC, and eradicates the northern tribes of Israel. Both covenants Abrahamic and Mosaic come to play into that passage.