Jonah is a little book accentuating God's mercy. It is an act of mercy on God's part to send Jonah to Nineveh. It is an act of God's mercy to rescue rebellious Jonah from the depths of the sea. It is an act of God's mercy to recommission Jonah after his flagrant disobedience. It is, of course, an incredible display of God's mercy to forgive the people of Nineveh. And, at the end of the book, it is merciful for God to deal with Jonah as His child rather than condemning Him. All along the line, "mercy triumphs over judgment" (James 2:13). And so, the Book of Jonah teaches us God's strong bias toward and His penchant for mercy.
In light of this lesson, what are we to do? Note Luke 18:13, "And the publican, standing afar off, would not lift up so much as his eyes unto heaven, but smote upon his breast, saying, God be merciful to me a sinner." This posture needs to be Jonah's and ours. "Therefore let us draw near with confidence to the throne of grace, so that we may receive mercy and find grace to help in time of need" (Hebrews 4:16).
Understanding this central thread puts us in a position to preach Christ from Jonah. Our Lord Jesus is the epitome of God's mercy. Note how Peter connects Christ with mercy extended to us. "Blessed be the God and Father of our Lord Jesus Christ, who according to His great mercy has caused us to be born again to a living hope through the resurrection of Jesus Christ from the dead" (1 Peter 1:3). On this same basis, we may preach Christ from Jonah.