Rashi on Deuteronomy 11:28/רש"י על דברים י״א:כ״ח

1מן הדרך אשר אנכי מצוה אתכם היום ללכת וגו׳ [IF YE DEPART] FROM THE WAY WHICH I COMMAND YOU THIS DAY, TO GO [AFTER OTHER GODS] etc. — You thus learn that he who serves idols departs from the entire path of life that Israel has been commanded. From this passage they (the Rabbis) taught the well-known dictum that he who acknowledges the divinity of an idol is as though he denied the Torah in its entirety (Sifrei Devarim 54:4).