Charles Ellicott Commentary Exodus 29:4

"And Aaron and his sons thou shalt bring unto the door of the tent of meeting, and shalt wash them with water." — Exodus 29:4 (ASV)

Aaron and his sons you shall bring to the door ... — The place of the laver, not yet mentioned, but designed in God’s counsels, was between the brazen altar and the Tabernacle (Exodus 30:18), and consequently near the door of the latter. Rabbinical tradition says that it was not placed exactly opposite the door, but a little towards the south side of the court.

And you shall wash them. —This is the first mention in Scripture of a religious ablution. Water is so natural a symbol of purity, and ablution so apt a representative of the purging from sin, that we can feel surprise neither at the widespread use of the symbolism in religions of very different characters, nor at its adoption into the system at this time imposed by Divine Providence upon the Hebrews. As it was to maintain its place even in the Divinely-appointed ceremonial of Christianity, it must have been à fortiori suitable for the earlier and less spiritual dispensation.

The widespread employment of it in other religions—e.g., in Egypt (Herod. ii. 37); in Persia (Zendavesta, 8 p. 271. Spiegel’s translation); in Greece (Döllinger, Jew and Gentile, vol. i., p. 220); in Italy (Dict. of Greek and Rom. Antiq., p. 719), and elsewhere—was no argument against its adoption into the Mosaic ceremonial, since the Divine legislation of Sinai was not intended to annul or supersede natural religion, but only to improve and expand it.