Having written ? in Pasuk 13 - ?Va'teatzar ha?Mageifah?, why does the Torah need to repeat ?ve?ha?Mageifah Ne?etzarah??
Seforno: Refer to 17:13:1:2. To teach us that thos who were initially affected by the plague were cured.
Why did Aharon return to Moshe?
Moshav Zekenim (citing R. Yehudah ha'Chasid): To inform him that the plague had ceased, so that he should stop Davening. 1
Moshav Zekenim (Ibid.)": We learn from here that, if a Choleh for whom one is Davenning recovers, one should stop Davenning. That being the case, how could Rashi in Yisro Sh'mos, 19:8, citing the Pesikta, learn from here that it is correct for a Shali'ach to return to the Meshale'ach, even if the latter knows what happened? Perhaps here it is to teach us that one stops Davening? (PF).