Idolatry and adultery are the same sin. The Mekhilta DeRabbi Yishmael, a 3rd-century CE halakhic midrash (rabbinic interpretive commentary), makes this case by pointing to the structure of the Ten Commandments themselves — and the parallel is not metaphorical. It is architecturally embedded in the tablets of stone.
The commandment "There shall not be unto you any other gods in My presence" sits on one tablet. Directly opposite it, on the second tablet, sits "You shall not commit adultery." The Mekhilta argues this positioning is deliberate. God arranged the commandments so that worshipping foreign gods and betraying a spouse would face each other across the stone — because Scripture considers them identical crimes.
The prophets made the same equation. Ezekiel compared Israel to "the adulterous woman, who though living with her husband, still takes strangers" (Ezekiel 16:32). The prophet Hosea received perhaps the most shocking prophetic command in the entire Hebrew Bible: "Go and love a woman beloved by her husband, and playing the harlot" (Hosea 3:1). God told Hosea to marry an unfaithful woman specifically so that Hosea would understand — in his own body, in his own heartbreak — what it feels like when Israel chases after other gods.
The Mekhilta's teaching reframes both commandments. Adultery is not merely a social crime. It is a spiritual betrayal that mirrors the ultimate spiritual betrayal: abandoning the God who chose you. And idolatry is not merely a theological error. It carries the same intimate sting as discovering your spouse in the arms of a stranger. The tablets were carved to make this impossible to miss.