If I forget thee, O Jerusalem - The meaning here is, that to sing in such circumstances would seem to imply that they had forgotten Jerusalem; that they were unmindful of its sorrows, and cared not that it was desolate. The remembrance of its calamities pressed hard upon them, and they could not do anything which would seem to imply that they had become unmindful of the sufferings that had come upon their nation. One will not make merry when a wife or child lies dying - or on the day of the funeral - or over the grave of a mother. A joyous and brilliant party, accompanied with music, feasting, dancing, when a friend has been just laid in the grave, when the calamities of war are abroad, when the pestilence is raging in a city, we feel to be untimely, unseemly, and incongruous. So these captives said it would be if they should make merry while their temple was in ruins; while their city was desolate; while their people were captives in a foreign land.
Let my right hand forget her cunning - Let my right hand forget its skill in music - all its skill. If I should now play on the harp - as indicative of joy - let the hand which would be employed in sweeping over its strings become paralyzed and powerless. Let the punishment come where it would seem to be deserved - on the hand which could play at such a time. So Cranmer held the hand which had been employed in signing a recantation of his faith in the fire, until it was burned off, and dropped in the flames.