Tafsiran Bilangan 27:21: Rashi, Avi Ezer, Or HaChaim & Rabbeinu Bahya

ולפני אלעזר הכהן יעמד AND HE SHALL STAND BEFORE ELEAZAR THE PRIEST — Here you have the request that you have made: that this honour should not depart from your father’s house, for Joshua, too, will need Eleazar (Midrash Tanchuma, Pinchas 11).

"And all the children of Israel concerning something that was a general principle for everyone, etc."Since the language is duplicated, 'and all the children of Israel and the entire congregation,' therefore, the Rabbi explains that 'the entire congregation' refers to those who were designated in the Tent of Meeting for a specific task upon them. 'And all the children of Israel' pertains to something that applies to the entire nation of Israel. Although we find in the scripture 'the children of Israel' being explained as 'the entire congregation' in the portion of Shelach Lecha, and there the commentators provided a suitable reason, here this reason does not apply.

על פיו יצאו, "at his command they will go out (to war), etc." This was a reference to Moses having said that a leader must be capable of commanding the people to follow him, i.e. ואשר יוציאם. All of this would occur after Eleazar had obtained G'd's approval through consulting the Urim VeTumim, the breastplate of the High Priest whose letters would flash in answer to questions posed to G'd.

ושאל לו AND HE SHALL ASK OF HIM, whenever he finds it necessary to go forth to war (cf. Targum Jonathan on).