Albert Barnes Commentary Exodus 20:22-26

"And Jehovah said unto Moses, Thus thou shalt say unto the children of Israel, Ye yourselves have seen that I have talked with you from heaven. Ye shall not make [other gods] with me; gods of silver, or gods of gold, ye shall not make unto you. An altar of earth thou shalt make unto me, and shalt sacrifice thereon thy burnt-offerings, and thy peace-offerings, thy sheep, and thine oxen: in every place where I record my name I will come unto thee and I will bless thee. And if thou make me an altar of stone, thou shalt not build it of hewn stones; for if thou lift up thy tool upon it, thou hast polluted it. Neither shalt thou go up by steps unto mine altar, that thy nakedness be not uncovered thereon." — Exodus 20:22-26 (ASV)

Nothing could be more appropriate as the commencement of the book of the covenant than these regulations for public worship. The rules for the building of altars must have been old and accepted, and are not inconsistent with the directions for the construction of the altar of the court of the tabernacle (Exodus 27:1–8) .