‘And YHWH said, “You have had regard for the gourd, for which you have not laboured, nor made it grow, which came up in a night, and perished in a night, and should not I have regard for Nineveh, that great city, in which are more than one hundred and twenty thousand persons who cannot discern between their right hand and their left hand, and also much cattle?”
YHWH then applies the object lesson that He has been building up to. He pointed out to Jonah that he had become so grateful for the helpless gourd and what it had done for him, that he had become greatly concerned for it, even though it was only a weak, natural object and one which Jonah had not even laboured over or caused to grow. Its destruction had moved him to compassion. (It is often strange what human beings can become over-fond of). Was it not then reasonable that He, YHWH, Who had created the weak Assyrians and their animals, and had caused them to grow, should be equally concerned for them, especially when he considered how much they depended on Him. For if Jonah would but consider the situation he would recognise that Nineveh contained over one hundred and twenty thousand people who could not discern their right hand from their left, in other words who were rather ignorant and helpless people, at least religiously speaking, (or possibly children under a certain age), on whom he should have pity because of their helplessness and need, as well as being a city which had a large number of helpless cattle. The mention of the cattle emphasises the weakness of what He is referring to. And they were ‘natural' things like the gourd which Jonah had had compassion on. And it was these who were benefiting by God's mercy and compassion. Was that then so wrong? Thus His rebuke of Jonah was because he had no concern for the weak and needy. He who had had compassion on a mere gourd, was lacking in compassion and mercy when it came to men and women (even if they were Assyrians).
Thus the central message of the prophecy of Jonah is precisely this, that God is of such a nature that He has mercy on all who are weak and admit their weakness, (whoever they are), when they truly turn from sin and seek Him in repentance and faith, a situation which all should be concerned to bring about. This was a vitally important message in 8th century BC Israel for in that land were many Canaanites and followers of false religions (such as Baalism) who needed to know that God had a welcome for them if only they would repent, turn from sin and seek His face.
Indeed the fact is often overlooked that the existence of a prophet like Jonah (and Elijah and Elisha) was proof positive that in the northern kingdom true worship was being continued apart from the Temple at altars presumably set up by the prophets. That was why Elijah had been able to ‘repair the altar of YHWH that had fallen down' (1 Kings 18:30) and had spoken of other altars wrongly destroyed by the Baalists (1 Kings 19:10). We may assume that they were altars set up under the provisions of Exodus 20:24-26. It was partly in order to win adherents to the worship at these altars that the prophecy of Jonah was written, with a promise that anyone of any nation could come and find acceptance if they came in repentance and faith, in the same way as the mariners and the Assyrians had.