Yahweh permitted His people to build altars where He granted special theophanies, that Isaiah , manifestations of His presence. [1] These were in addition to the altars at Israel"s central sanctuary (the tabernacle and later the temple; cf. Judges 6:25-27; Judges 13:15-20; 1 Samuel 9:11-14; 1 Samuel 16:1-5; 1 Kings 18:30-40). They were to build these altars for formal worship and for special occasions (e.g, Joshua 8:30; Judges 6:25-26) out of earth or uncut stone. The Canaanites used cut or "dressed" stone for their altars, and it was probably to distinguish the two that God directed Israel as He did. [source][source][source]
Israel"s altars were not to have steps, as many Canaanite altars did, so the naked flesh of the priests might not appear as they mounted them to make their offerings. [source][source][source]
"Possibly the verse intends to oppose the practice of certain peoples in the ancient East, like the Sumerians for instance, whose priests ... used to perform every ritual ceremony in a state of nakedness. Likewise the Egyptian priests ... used to wear only a linen ephod, a kind of short, primitive apron." [2][source]
"This simple description of true worship is intended to portray the essence of the Sinai covenant in terms that are virtually identical to that of the religion of the patriarchs-earthen altars, burnt offerings, and simple devotion rather than elaborate rituals. A simple earthen altar is sufficient. If more is desired (e.g, a stone altar), then it should not be defiled with carved stones and elaborate steps. The ultimate purpose of any such ritual is the covering of human nakedness that stems from the Fall ( Exodus 20:26 b; cf. Genesis 3:7). The implication is that all ritual is only a reflection of that first gracious act of God in covering human nakedness with garments of skin ( Genesis 3:21)." [3][source]