25 On the following day the Book of Jonah was read according to custom, after the completion of which I began this discourse. A book has been read, brethren, in which it is foretold that sinners shall be converted. Their acceptance takes place because that which is to happen is looked forward to at present. I added that the just man had been willing even to incur blame, in order not to see or denounce the destruction of the city. And because the sentence was mournful he was also saddened that the gourd had withered up. God too said to the prophet: “Are you sad because of the gourd?” and Jonah answered: “I am sad.” And the Lord then said, that if he grieved that the gourd was withered, how much should He Himself care for the salvation of so many people. And therefore that He had put away the destruction which had been prepared for the whole city.
Source: Letters (New Advent)