Jeremiah 26:3

He did not use the word perhaps out of ignorance, aware as he was of their disobedience. Instead, he expressed such uncertainty to avoid their taking note of the divine sentence and despairing of salvation. It resembles also what was said by Ezekiel, "If then …

Jeremiah is also instructed to speak to all the cities of Judah, although the Septuagint does not translate the word cities, lest it seem indecorous to speak to cities from the court of the house of the Lord, to which they are not present. Yet, when he addresses the people and the citizens, he speaks to the cities themselves. And he stands beautifully in the court and the vestibule of the temple of the Lord, that the people may be brought together to hear the words of the prophet through the occasion of praying to the Lord and adoring him. "Do not remove a word," he is told, even though it may be sorrowful, even though your audience may be incited to rage against you, nevertheless speak what you have been commanded to say, not yielding to the fear that they will persecute you but only to the rule of the Lord! "Perhaps," he thinks, "they will listen and be converted." However, an ambiguous word like "perhaps" cannot be reconciled with the majesty of the Lord but speaks instead of our desire that human free will be served and that it not be compelled from the Lord's foreknowledge, as though of necessity, either to act or to refrain from acting. For it is not because God knows the future that the future comes about, but it is because of what will happen that God knows it before it occurs. Nevertheless, Jeremiah knew that if the Lord warned of bad consequences and the people did penance, they would be repenting for the sake of what the Lord threatened to do to them. Likewise, if the Lord had promised prosperity and the people then acted with negligence, God would exchange the favorable outcome for a bad one. Such is what is also found in the Gospel: "I will send my son; perhaps they will respect him," spoken indeed from the person of the omnipotent God. […]

But if one says that God revoked that severe sentence in consideration of their penitence, according to what he says by Ezekiel, "If I say to the wicked, 'You will surely die' and he becomes penitent for his sin and does judgment and justice … he shall surely live; he shall not die," we are similarly taught that we should not be obstinate in our resolve, but that we should with gentle pity soften down the threats that necessity called forth. That we may not conclude that the Lord granted this specially to the Ninevites, he continually affirms by Jeremiah that he will do the same in general toward all and promises that without delay he will change his sentence in accordance with what we deserve, saying, "I will suddenly speak against a nation and against a kingdom to root out and to pull down and to destroy it. If that nation repents of the evil which I have spoken against it, I also will repent of the evil which I thought to do to them. And I will suddenly speak of a nation and a kingdom, to build up and to plant it. If it shall do evil in My sight, that it obey not my voice: I will repent of the good that I thought to do to it." To Ezekiel also: "Leave out not a word, if so they will hearken and be converted every one from his evil way that I may repent of the evil that I thought to do to them for the wickedness of their doings." And by these passages it is declared that we ought not obstinately to stick to our decisions but to modify them with reason and judgment, and that better courses should always be adopted and preferred and that we should turn without any delay to that course that is considered the more profitable. […]

If so be they will hearken,....

This was the main thing God intended in sending him to them, to try if they would return from their sins, that so God might turn from his anger and turn away the judgments that threatened them, which he was not only willing, but very desirous to do, as soon as he could do it without prejudice to the honour of his justice and holiness.