Adam Clarke on Nehemiah 3:1

Eliashib the high priest - It was right that the priests should be first in this holy work; and perhaps the sheep gate which is mentioned here is that by which the offerings or sacrifices were brought into the temple.

They sanctified it - As they began with the sacred offering as soon as they got an altar built, it was proper that the gate by which these sacrifices entered should be consecrated for this purpose, i. e., set apart, so that it should be for this use only.