Jonah 3:4

And Jonah began to enter into the city a day's journey That is, he proceeded into the city as far as he could go in a day. And he cried, Yet forty days and Nineveh shall be overthrown The threat is express; but there was a reserve with God on condition of repentance. And it must be observed, that in most of the threatenings of God there is a condition expressed or understood. This is the general rule for interpreting all such denunciations, as has been observed in the note on Jeremiah 18:8, unless where God makes an express declaration that the iniquity of the people against whom he denounces his judgments is full, and that he will not spare them; or, as it is expressed by our Saviour, with regard to Jerusalem, that the things which belong unto their peace are then hid from their eyes.