This was probably an old formula, the sense of which, on its ethical side, is comprised in the first and second commandments.
Shall be utterly destroyed - The Hebrew word here used is חרם châram (i. e. devoted). See Leviticus 27:28.

Utterly destroyed - The word חרם cherem denotes a thing utterly and finally separated from God and devoted to destruction, without the possibility of redemption.

He that sacrificeth unto any god,.... To Elohim, to strange gods, to the idols of the people, as the Targum of Jonathan; to the Egyptian deities, to the gods of the Moabites, Amorites, Edomites, Canaanites, Philistines, or any other: Aben Ezra says the word Elohim comprehends angels; and by the exceptive clause it is plain it takes in all that had been, were, or ever would be the objects of idolatrous worship, especially the sun, moon, and stars, the principal objects of worship in those days:
save unto the Lord only; the true and living God; Jehovah, the self-existent, immutable, and eternal Being; the Creator of all things, the possessor of heaven and earth, the most high God, and the only one: sacrificing takes in all the acts of service performed to an idol as to the true God, as offering incense, pouring out a libation, as well as slaying and burning an animal as Jarchi observes: he shall be utterly destroyed; be accursed, anathematized, devoted to destruction, as the word used signifies: the Targum of Jonathan is,"he shall be killed with the sword, and his goods consumed,''not only lose his life but his substance, and so be destroyed in body and estate.

Whoever offered sacrifice to strange gods instead of to Jehovah alone, was liable to death. יחרם he shall be banned, put under the ban (cherem), i.e., put to death, and by death devoted to the Lord, to whom he would not devote himself in life (cf. Leviticus 27:29, and my Archologie, 70).