One of my favorite books in the whole bible is Jonah; not because of some fascination with a man being swallowed by a giant fish. The account of Jonah fascinates me because of the message of God's love for the world, His mercy and grace towards sinners, and the missional aspect of this book.
Jonah, knows that God is a God of grace and mercy (4:1). Because he doesn't want the violent and oppressive people of Nineveh, enemies of Israel, to experience this grace, he directly disobeys the command of God to go to Nineveh and preach against that city. The book is mostly about a prophet who disobeys God, and it ends with the prophet as the 'bad guy' and God Himself is the 'good guy'. Jonah wants the benefits of living under God's grace to remain with Israel, and cannot stomach the possibility that God might show grace to a very brutal and ruthless enemy, an enemy who could possibly obliterate Israel. Jonah basically tells God, "I told you so!" when the whole city of Nineveh repents, then goes outside the city to watch and see what will happen (obviously hoping that God will destroy the city). In the climax of the entire book, God reprimands Jonah for his persisting callousness and short-sightedness. The book closes when God says, "And should I not pity Nineveh, that great city, in which there are more than 120,000 persons who do not know their right hand from their left [i.e., 'right from wrong'], and also so much cattle?"
The point is simply that God says, "I will have mercy on whom I have mercy, and I will have compassion on whom I have compassion." (Ex. 33:19; Romans 9:15). We serve a God who is the Covenant Lord of the Universe. Salvation is the grace of God, not deserved by the religious, the good, or the chosen. Missions is the right response to that grace...driven by the fact that no one deserves it, but that God Himself will save...even if He uses sinful people to proclaim the message.