Matthew 5:27 → Exodus 20:14

The second antithesis of the Sermon on the Mount cites the seventh commandment from Exodus 20:14 — "Do not commit adultery" (lo tina'af) — and then radicalizes its application to the internal act of lustful desire. Jesus's formulation "anyone who looks at a woman to lust after her has already committed adultery with her in his heart" exposes the Decalogue's concern with the interior life, not merely outward behavior. The Tenth Commandment had already prohibited coveting a neighbor's wife, showing that the Decalogue itself was never satisfied with external compliance alone. Jesus, speaking with his own sovereign authority ("but I tell you"), does not contradict Moses but fulfills the law's deepest intention by revealing that adultery begins in the heart — the very realm where the new covenant promises transformation (Jeremiah 31:33; Ezekiel 36:26-27). This antithesis thus demonstrates how Jesus completes the law by internalization rather than mere external extension.