John Calvin Commentary Jeremiah 17:15

"Behold, they say unto me, Where is the word of Jehovah? let it come now." — Jeremiah 17:15 (ASV)

Here Jeremiah complains of the obstinate contempt of the people; he found them not only discourteous but even petulant towards God, so that they did not hesitate to discredit all prophecies, to despise the promises, and boldly to reject all threats. The Prophet had often threatened them; and when God delayed the time, they made a wrong use of His forbearance, as is commonly the case with the reprobate. Nor did they consider it enough even to add sins to sins, but they openly and petulantly provoked God, saying, “Where is the word? Many years have now elapsed since you have continually spoken of war, of famine, and of pestilence; but we still remain quiet, and God spares us; where then is the word of Jehovah, which you have announced?”

We now see then how great was the willfulness of this people, for the teaching of Jeremiah became not only useless but was treated with ridicule. They had, however, heard much before from the mouth of Isaiah:

“Alas! When the Lord calls you to ashes and sackcloth, you say, ‘Let us eat and drink, for tomorrow we shall die.’ ‘As I live,’ says the Lord, ‘this iniquity shall not be forgiven to you.’”
(Isaiah 22:12–14)

God then had sworn by His own glory that their sin would be inexpiable, because they continued obstinately in their vices and were not at all terrified by the threats of the prophets. We see, however, that they grew ever worse.

Isaiah was dead when they spoke in this way in contempt and mockery, “Where is the word of Jehovah? Let it now come!”—as though they intentionally provoked God, like one who despises his enemy and says, “Oh! You are indeed to be dreaded, if you are to be believed! Let us now see your power; show us what you can do.” With such contempt did they utter their scoffs, when God, through His servants, made known to them the approaching ruin they deserved. In short, we see that the Prophet shows here that they had come to a hopeless state.