Psalms 137:2

We hanged our harps upon the willows, in the midst thereof. These are, not without great probability, supposed to be the words of some holy Levites, who had been accustomed to music, both vocal and instrumental, in the service of the temple. Harps are here put, by a synecdoche, for all instruments of music. It is further to be observed, that although the harp was used by the Greeks in mourning, yet it was used by the Hebrews in rejoicing, as is manifest from Genesis 31:27; 2 Chronicles 20:27; Psalms 43:4. This passage is to be understood, either, 1st, Figuratively, signifying only, that they abandoned all signs and means of comfort; or rather, 2d, Properly, as the songs are which the Babylonians required them to sing to their harps, Psalms 137:3. Upon the willows Which commonly grow upon the banks of rivers, as they did on the banks of the Euphrates, in such an abundance that from thence it is called the brook, or torrent, or river, (as נחל may be properly rendered,) of willows, Isaiah 15:7. Thus “the sincere penitent, like these captives, hath bidden adieu to mirth; his soul refuseth to be comforted with the comforts of Babylon; nor can he sing any more till pardon and restoration shall have enabled him to sing in the temple a song of praise and thanksgiving.”