Charles H. Spurgeon on Psalms 137:7

Remember, O LORD, the children of Edom, etc. The Jews were their brethren: Ob 1:10 Am 1:11. They were their neighbours, Idumea and Judea bordered upon one another: Mr 3:8. They were confederates with the Jews (Jer 27:3: an Edomitish ambassador was at Jerusalem), who, together with the ambassadors of the other kings there mentioned, were strengthening themselves with Zedekiah against Nebuchadnezzar; see Ob 1:7. For them, therefore to revenge themselves for former wrongs done them upon the Jews, and that in the day of their calamity, this made their sin exceedingly sinful —William Greenhill, 1591-1677.