Albert Barnes Commentary Numbers 27:21

"And he shall stand before Eleazar the priest, who shall inquire for him by the judgment of the Urim before Jehovah: at his word shall they go out, and at his word they shall come in, both he, and all the children of Israel with him, even all the congregation." — Numbers 27:21 (ASV)

And he shall stand before Eleazar the priest ... - Joshua was thus to be inferior to what Moses had been. For Moses had enjoyed the privilege of unrestricted direct contact with God; Joshua, like all future rulers of Israel, was to ask counsel indirectly, through the High Priest and those means of inquiring of God with which the high priest was entrusted. Joshua seems to have neglected to seek such counsel when he concluded his hasty treaty with the Gibeonites (Joshua 9:3 and following).

Judgment of Urim - See Exodus 28:30 note.