Albert Barnes Commentary Exodus 22:20

"He that sacrificeth unto any god, save unto Jehovah only, shall be utterly destroyed." — Exodus 22:20 (ASV)

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.