What is the significance of "va'Ye'tar El Hashem" (as opposed to 'va'Yispalel El Hashem')?
Riva: Because Hashem gives and does not take. Moshe wanted Hashem to take back every animal (and subsequently, every locust (10:17-19), to prevent the Egyptians from benefiting from the hides and from the locusts. Therefore, he needed a strong Tefilah to remove these two Makos.
Gur Aryeh (to 8:5): Rashi bases this on grammar. Here, the verb Ayin-Tav-Resh is in simple form, whereas elsewhere in the Makos (e.g. 8:5, 8:24) it is in causative form (Hif'il). That is why Rashi to 8:5 explains "to increase prayers" - in quantity; whereas here he translates "he exerted himself in prayer" - in intensity. (CS)
Knowing that Pharaoh would retract (seeing as all ten plagues were hinted on his staff), why did Moshe immediately agree to Daven on Pharaoh's behalf?
Oznayim la'Torah: Because Hashem commanded him to do so - to remove one plague in order to bring on the next one, until all ten plagues had been carried out.
