This verse begins by describing what happened when Jonah reached the large city of Nineveh. Jonah started through the city, that is, began to walk through it, but did not start to proclaim his message until he had walked one day’s journey, presumably not halfway to the other side. Only then did he proclaim his message: “In forty days Nineveh will be destroyed!” New English Bible, no doubt intentionally, uses the verb “overthrown,” to correspond to the verb used in Hebrew, which is the same as that associated with the destruction of the cities of Sodom and Gomorrah in Gen 19.21-29. It is also used in Jer 20.16; Lam 4.6, and generally God is the subject when the reference is to the destruction of a city, usually in some violent manner (compare Amos 4.11, and the imagery of God “overturning” Jerusalem in 2 Kgs 21.13). Winding Quest translates suitably, “this city will become a heap of ruins.” Nowhere else in the book is there a proclamation or announcement by Jonah, and we hear nothing more of him in this chapter.
Jonah’s only message to the people of Nineveh consisted of the unconditional assertion that only forty days remained before the total destruction of their city, or “within forty days Nineveh will have been overthrown.” The expression forty days is often used in the Bible as a round number; for example, Exo 24.18; 34.28; Num 13.25; 1 Sam 17.16; 1 Kgs 19.8, where most scholars believe that an exact period is not intended. It is clear from the mention here of Jonah’s single day’s journey, using the same kind of expression as in the previous verse, that the reference in verse 3 must be to the diameter of the city and not to its circumference.
It is frequently necessary to indicate clearly who are the persons who received the proclamation announced in verse 4. Therefore it may be necessary to say “he proclaimed to the people,” or “he announced to the inhabitants of the city,” or “… to those who lived there.”
No reason is given to the people for the threat of destruction and no alternative of repentance is offered. It is as though Jonah is only concerned to carry out his commission to the absolute minimum, and he seemingly has no concern for the well-being of those to whom he preached.
In a number of languages the method of destruction must always be indicated by a verb such as destroyed; for example “conquered by an enemy,” “destroyed by fire,” or “leveled by an earthquake.” The most generic expression may simply be “will not exist any longer.” In this context such a general statement may be preferable, for it would be reading a good deal into the text to suggest the specific way in which Nineveh would be destroyed.
Quoted with permission from Clark, David J. et al. A Handbook on the Book of Jonah. (UBS Helps for Translators). New York: UBS, 1978, 1982, 1993. For this and other handbooks for translators see here .