If I forget thee, O Jerusalem, let my right hand forget [her cunning].
Ver. 5. If I forget thee, O Jerusalem] As I might seem to do, should I herein gratify these idolaters; or otherwise obey them, rather than God. The Jews at this day, when they build a house, they are, say the Rabbis, to leave one part of it unfinished and lying rude, in remembrance that Jerusalem and the temple are at present desolate. At least, they use to leave about a yard square of the house unplastered, on which they write, in great letters, this of the psalmist, "If I forget Jerusalem," &c., or else these words, Zecher leehorban, that is, The memory of the desolation (Leo Modena of the Rites of the Jews).
Let my right hand forget] Fiat abalienata atque emortua, Let it be paralytical and useless, unfit to touch the harp.