Learn, thou, therefore, to rehearse and impress upon thine own heart, and on the hearts of others also, this repeated conclusion of each verse; that it may be a bulwark for thee against the devil, who is ever maliciously jeering our temptations, and saying, that it is not the _mercy_ of God, but his _judgment_, that “endureth for ever.” Hypocrites and enthusiasts sing not, nor can sing, this blessed conclusion of the verses, “For his mercy endureth for ever.” They can only sing, ‘For our goodness endureth for ever.’ But do thou, Christian brother, hold fast this doctrine of a Davidical heart; the truly divine and heavenly doctrine of the remission of sins; a remission “enduring for ever,” and which sin can never destroy; which alone overcomes the devil and all errors, and which alone can give the conscience rest under all temptations, and the agonizing conflicts of death. PSALM CXXXVII. _The constancy of the Jews in captivity.—The prophet curseth Edom and Babel._ By the rivers of Babylon, there we sat down, yea, we wept, when we remembered Zion. We hanged our harps upon the willows in the midst thereof. For there they that carried us away captive required of us a song; and they that wasted us _required of us_ mirth, _saying_, Sing us _one_ of the songs of Zion. How shall we sing the LORD’S song in a strange land? If I forget thee, O Jerusalem, let my right hand forget _her cunning_. If I do not remember thee, let my tongue cleave to the roof of my mouth; if I prefer not Jerusalem above my chief joy. Remember, O LORD, the children of Edom in the day of Jerusalem; who said, Rase _it_, rase _it, even_ to the foundation thereof. O daughter of Babylon, who art to be destroyed; happy _shall he be_, that rewardeth thee as thou hast served us. Happy _shall he be_, that taketh and dasheth thy little ones against the stones. This Psalm is a prayer in the persons of the captives of Babylon; whether we understand it as having been written after the captivity, or before it in the way of prophecy. The captives here pray for the city of Jerusalem; that is, for the place of the word and the worship of God; for all these things had been destroyed by the Babylonians.