Rashi on the Prophets and Writings
Psalms 51
Why do you boast of evil, you mighty man? Why do you boast and brag of the evil that you do, you who are mighty in Torah? God’s kindness is constant to rescue the one whom you pursue. Another explanation: God’s kindness is constant. Had Ahimelech not given me bread, do you think that I would have died of hunger? God always shows kindness toward Israel, and if he had not given me [to eat], others would have given me.
sharpened Heb. מְלֻטֳשּׁ. working deceit Cutting the flesh with the hair.
shall tear you down Heb. יתצך, an expression of demolition (נתיצה). He will break you Heb. יחתך, an expression of breaking. and pluck you Heb. ויסחך, and shall tear you out. and uproot you He shall uproot after you, to tear out all the roots; esraciner or esraziner in Old French, to uproot, deraciner in modern French.
and laugh at him And this is the ridicule they will say about him: “Behold! This is the man who does not place his trust in the Holy One, blessed be He. See what happened to him.”
he strengthened himself in his wickedness Heb. יעז בהותו.
But I who am now being pursued by you, will be like an olive tree, fresh with children and grandchildren, in the house of the Holy One, blessed be He.
when You have done [this] When You do this for me. This verse is addressed to the Holy One, blessed be He.
You arrive at the cited line; the whole work is yours to read around it. The text is set from the cited public-domain edition.