| Barnes' Notes on the Bible The prophet was directed to let the people see him sighing and prostrate, as a sign of the sorrow and weakness about to come upon the people. The breaking of thy loins - The prostration of strength; the loins being the seat of strength.
Clarke's Commentary on the BibleSigh - with the breaking of thy loins - Let thy mourning for this sore calamity be like that of a woman in the pains of travail.
Gill's Exposition of the Entire BibleSigh, therefore, thou son of man, with the breaking of thy loins,.... As if thy loins were broke, and go as if they were, and sigh as thou goest; or as a woman in travail, having her hands upon her loins as ready to break, and in the utmost distress; or heave, and groan, and sigh, till the girdle of the loins is broke, and by these motions and gesture show the miserable state of this people, and how much thou art affected with it: and with bitterness sigh before their eyes; in the sight and hearing of the captives at Babylon; who would take care, by some means or other, to inform their brethren at Jerusalem of it, how the prophet sighed and groaned, under an apprehension and assurance of a dreadful calamity coming upon them; using along with his sobs and sighs, and brinish tears, doleful words and bitter lamentations.
Geneva Study BibleSigh therefore, thou son of man, with breaking {d} heart; and with bitterness sigh before their eyes. (d) As though you were in extreme anguish.
Wesley's Notes 21:6 Sigh therefore - Thereby express deep sorrow. Breaking of thy loins - Like a woman in travail.
Jamieson-Fausset-Brown Bible Commentary6. with the breaking of thy loins-as one afflicted with pleurisy; or as a woman, in labor-throes, clasps her loins in pain, and heaves and sighs till the girdle of the loins is broken by the violent action of the body (Jer 30:6).
Matthew Henry's Concise Commentary21:1-17 Here is an explanation of the parable in the last chapter. It is declared that the Lord was about to cut off Jerusalem and the whole land, that all might know it was his decree against a wicked and rebellious people. It behoves those who denounce the awful wrath of God against sinners, to show that they do not desire the woful day. The example of Christ teaches us to lament over those whose ruin we declare. Whatever instruments God uses in executing his judgments, he will strengthen them according to the service they are employed in. The sword glitters to the terror of those against whom it is drawn. It is a sword to others, a rod to the people of the Lord. God is in earnest in pronouncing this sentence, and the prophet must show himself in earnest in publishing it. | 
