John Calvin Commentary Isaiah 21:3

"Therefore are my loins filled with anguish; pangs have taken hold upon me, as the pangs of a woman in travail: I am pained so that I cannot hear; I am dismayed so that I cannot see." — Isaiah 21:3 (ASV)

Therefore are my loins, filled with pain. Here the Prophet represents the people as actually present. This was because it was not enough to have simply foretold the destruction of Babylon; he also needed to confirm the belief of the godly in such a way that they felt as if the actual event were placed before their eyes. Such a representation was necessary. The Prophet does not here describe the feelings of his own heart, as if he had compassion on the Babylonians; rather, as we have said before, he temporarily assumes the character of a Babylonian.

It ought undoubtedly to satisfy our minds that the hidden judgments of God are held out to us, as in a mirror, so that they may arouse our sluggish faith. Therefore, the Prophets describe with greater beauty and richness, and paint in lively colors, those things that exceed the capacity of our reason. The Prophet, by expressing his grief in this way, informs believers how awful God's vengeance is that awaits the Chaldeans, and how dreadfully they will be punished—just as we are struck with surprise and horror when any sad news is brought to us.

As the pangs of a woman that travaileth. He adds a stronger expression of grief when he compares it to that of a woman in labor—similar to how a person in fearful anguish turns every way and writhes in every part of his body. Such modes of expression are used by the Prophets because of our sluggishness, for we do not perceive God's judgments until they are pointed out, as it were, with a finger, and affect our senses. We are warned to be on our guard before they arrive.