Комментарий к Бамидбар 1:19

ויפקדם במדבר סיני, the reason why the Torah mentions the location of this count is because during the second such count in Numbers 26,3 the Torah mentions that it took place in the wilderness around Moav, prior to the assault on the land of Israel before crossing the Jordan river. At that time after the death of Aaron, Moses issued these instructions to Eleazar, Aaron’s son and successor.

V. 19. ויפקדם במדבר סיני durch diese Wiederholung ist vor Beginn der Zählung nochmals Begriff und Bedeutung derselben in Erinnerung gebracht (siehe zu V. 1).

כאשר צוה ה' את משה, “as the Lord had commanded Moses;” these words belong to verse 18, where Moses is reported as having assembled all the people. [I suppose our author found a sentence commencing with “as, כאשר,” as somewhat unusual. Ed.]

ויפקדם במדבר סיני, “he counted them in the desert of Sinai.” The tribes were counted there, one after another in the order in which their respective flags had been arrangedHe commenced the count with the eldest son of Yaakov, Reuven.