In Matthew 12:41, Jesus explains to a crowd that "the men of Nineveh will stand up at the judgement with this generation and condemn it; for they repented at the preaching of Jonah, and now something greater than Jonah is here." It may seem an odd comparison at first, given that Jonah was hesitant to bring God's warning to the people of Nineveh to the point that he ran from God, was cast overboard by sailors in an attempt to calm a wrathful storm, and was swallowed by a giant fish for several days. Jonah was hardly the epitome of a willing servant, yet that was likely Jesus' point.
By the time Jonah reached Nineveh, he had walked hundreds of miles, been cast into stormy seas and resided in a fish. His look, smell and earnest message were enough to convince an entire city to repent and be spared God's wrath, whether he was a hesitant helper or not. The generation of Jews questioning Jesus, however, had the sinless, miracle-invoking incarnation of God before them in Jesus. Yet they were hesitant to believe in his message. What had they missed? That the greatest act of love in history had occurred: God was willing to live like us through all the pain and joy in life. As a result, we too now have an opportunity to put our faith in him.