Psalm 137 was written by the rivers of Babylon, where the exiled Jews wailed and lamented the destruction of the Beit Hamikdash (Holy Temple). They wondered how they would continue to endure on foreign soil. How could they sing the songs of Hashem (God), which were supposed to be sung in the Temple, there? Their answer was an oath to never forget Yerushalayim (Jerusalem). This psalm makes an oblique reference to Deuteronomy 8:19, “If you do forget Hashem your God and follow other gods to serve them or bow down to them, I warn you this day that you shall certainly perish.” Israel’s exile came when they forgot God in their land. In Babylon, they promised themselves to never repeat that mistake, and to never forget Yerushalayim. Today, this psalm is recited at Jewish weddings just before the groom breaks a glass, ensuring that Jerusalem is always at the forefront of our minds and reminding us that no joyous occasion is complete until Yerushalayim is restored to its former glory.