When we read through the Old Testament, it is easy to get the impression that God is one of wrath and judgment. If one sifts through carefully, there is yet a God of grace. In the story of Jonah we can see the God of Grace more clearly.
Jonah was called to preach judgment to the wicked nation of Nineveh (Assyria). Jonah refused to go, and after a bout with a great fish, he gave in to God’s command. Why would God keep Jonah alive (often prophets would be stricken dead if they disobeyed God) to still send him to warn this wicked nation? Because of God’s love for the lost. Notice the Book of Jonah comes a little after the Book of Hosea, which is God’s plea for Israel to return to Him. After Israel (God’s chosen people) still reject God, He then pursues another nation, one that will turn to Him. This is akin to God’s call to the Gentile nations in the New Testament.
God saw potential in the Assyrians. And to no surprise to Jonah (though to his disappointment), Nineveh heeded the warnings of God. Although God did not specifically call Nineveh out of darkness, as God calls the Gentiles (church) in 1 Peter 2:9, nor did He establish a covenant like He did with Israel in Ex. 19, the people of Nineveh had a heart of repentance in light of warnings of judgment. Their hearts were wicked, but not hard.