By all accounts, Jonah’s message to Nineveh was succinct and brief. He does not appear to have engaged in long, standing sermons, but keeping it short so as to tell it as he went along through the city. It was long enough to catch ears as he walked in and out of their range of hearing. And yet, like all messages of salvation, the hearer to which it was directed already knew in their heart what they needed to do; they were already aware of the specific sin from which they needed to repent.
Extra-biblical historical evidence is plentiful in its revelation that the Assyrian Empire was particularly violent and brutal. These were not people that were merely “falling short” of following God’s commandments, but wholly engaged in pursuing violence in their worship, in their politics, in their dealings with others. Spiritually, they were really far down the road, so to speak; “scary” even. But upon seeing the walking proof in their streets that God revives sinners from even the lowest depths if they turn to Him in earnest and sincere repentance, the Assyrians immediately knew that each must not just merely “turn from his wicked way”, but “from the violence which is in his hands”, the worst conditions of sin imaginable, which each and every one of them was keenly aware.
This is why, in reality, you don’t have to have been a drug addict to witness to drug addicts, you don’t have to have been a criminal to witness to criminals, or possess any other such worldly “pre-qualification” for sharing the gospel to an individual or group from a background radically different from your own. We are ALL sinners. Other sinners already know what they need to repent of; they just need a sincere messenger to communicate it.†††