Psalms 137:2

“We hanged our harps upon the willows - The harps once used to accompany the songs of praise and the service of God in the temple; the harps with which they had sought to beguile their weary hours, and to console their sad spirits in their captivity. The word rendered “willows” - ערבים ‛ărâbiym - used only in the plural, denotes the willow or osier, so called from its white, silvery leaves. Gesenius, Lexicon. Compare Isaiah 15:7. It is probable that the weeping willow - the willow with long pendulous branches - is here referred to. Trees in desert lands spring up along the courses of the streams, and appear, in the wide desolation, as long and waving lines of green wherever the rivers wind…”

“Harps - Harps are here put for all instruments of musick. Psalms 137:3”

“137:2-4 Because the music of Jerusalem was tied to the joys of life in the Promised Land, the Exile removed any occasion for singing joyous songs. The Babylonians wanted the Judeans to sing and dance for them, but the exiles’ grief made doing so either distasteful or impossible. The songs celebrating the Lord speak of his power and goodness, but his people were filled with doubts and questions. They hung their harps in trees, perhaps signifying the death of their joy under God’s curse (Deut 21:23).”

“we hanged: Willows were so plentiful at Babylon, on the banks of the Euphrates, that Isaiah calls it "the brook or river of willows." Psa 33:2, Psa 81:2; Isa 24:8; Eze 26:13; Amo 8:10; Rev 18:22 Psalms 137:3”