Comentario sobre Exodo 8:5

התפאר עלי GLORY OVER ME — Similar is, (Isaiah 10:15) “Should the axe יתפאר against him that heweth therewith” i. e. should it boast, saying “I am greater than thou”; old French vanter. Therefore התפאר means pride yourself on showing your cleverness and on asking of me a difficult matter asserting that I shall be unable to do it.

L’MATHAI’ (AGAINST WHAT TIME) SHALL I ENTREAT FOR THEE? Rashi commented: “If the text said mathai (when) — [not l’mathai] — shall I entreat, it would signify ‘when shall I pray?’ But now that it said l’mathai, it means ‘Today I will pray for you that the frogs be destroyed by the time which you will set for me. Say then by what day you wish that they shall be destroyed.’”
In line with the plain meaning of Scripture, the removal of the plagues took place at the time of Moses’ prayer, as it is written, And Moses cried unto the Eternal, etc., and the Eternal did according to the word of Moses¹³²Verses 8-9. and it is not written “and the Eternal did so tomorrow.” The letter lamed in the word l’mathai is no proof that Moses prayed immediately, for the word l’mathai is equivalent to mathai, there being many verses where the lamed occurs [just for elegance of language], thus: ‘l’min’ (from) the day that thou didst go forth out of the land of Egypt;¹³³Deuteronomy 9:7. The lamed in the word l’min is superfluous. until ‘l’minchath’ (the offering) of the evening;¹³⁴Ezra 9:4. There the lamed in l’minchath is a superfluous style. the wing of the one cherub was five ‘l’amoth’ (cubits).¹³⁵II Chronicles 3:11. Here the lamed in l’amoth is superfluous. There are many other such cases.

התפאר עלי, arrogate to yourself the right to ask what you want of me and I shall carry out your wish. The construction is similar to Judges 7,2 פן יתפאר עלי ישראל לאמר ידי הושיעה לי, “lest Israel be arrogant enough vis-à-vis Me to say: ‘my hand has been strong enough to provide my own salvation.’”