וידי משה כבדים. בִּשְׁבִיל שֶׁנִּתְעַצֵּל בַּמִּצְוָה וּמִנָּה אַחֵר תַּחְתָּיו, נִתְיַקְּרוּ יָדָיו:
BUT MOSES HANDS BECAME HEAVY — Since he had been lax in [the performance of] the commandment [of warring against Amalek] and had appointed someone else in his stead, his hands became heavy.
וידי משה כבדים. מכאן שלא ישהה אדם במצות, אלולי שאמר משה ליהושע "בחר לנו אנשים" לא היה מצטער... באותה שעה כאדם שתלויין לו שני כדין של מים.
And Moshe’s hands felt heavy: (We learn) from here not to delay in performing Mitzvot. Had Moshe not instructed Yehoshua to choose men (for the battle), he would not have felt troubled...At that time Moshe (felt) like he was carrying two pitchers of water.
