Jonah 3:5

‘And the people of Nineveh believed God, and they proclaimed a fast, and put on sackcloth, from the greatest of them even to the least of them.'

But the impact of the message was huge, for the people responded to ‘God' with all their hearts. Note the change from ‘YHWH to ‘God'. They were responding to Jonah's God. They knew nothing of the covenant with YHWH. We do not know what humanly speaking had prepared their hearts for this message. Perhaps it was the recent plagues (which certainly occurred around this time). Perhaps it was bad news with respect to their war with Urartu, their northern neighbour, causing great fear among the populace. But whatever it was it was kick-started by Jonah's preaching, taking him totally by surprise. It would not have taken God by surprise. He had known what the situation was.

The impact may have been made all the greater by Jonah's ‘unearthly' appearance caused by his sojourn in the large fish, and have been backed up by rumours which were going around of how this strange prophet had come out of a large fish. In a superstitious age such factors would be very telling, and if war was looming it would have had an even greater impact. But, of course, in the end it was all due to YHWH. ‘Salvation is of YHWH.'

The result was that the people proclaimed a fast, and put on sackcloth, both of which were common evidences of mourning in the area. And it is stressed that this was done by the whole people. They were convicted of sin, and were seeking mercy.