Charles Ellicott 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)

After the judgment of Urim ... — See Exodus 28:30, and Note.

At his word ... — That is, Joshua and the children of Israel were to abide by the decision of the high priest, which was obtained by means of Urim and Thummim.