Says the pasuk [במדבר ט"ו כ"ג]:
אֵת֩ כׇּל־אֲשֶׁ֨ר צִוָּ֧ה יְ-הֹ-וָ֛-ה אֲלֵיכֶ֖ם בְּיַד־מֹשֶׁ֑ה מִן־הַיּ֞וֹם אֲשֶׁ֨ר צִוָּ֧ה יְ-הֹ-וָ֛-ה וָהָ֖לְאָה לְדֹרֹתֵיכֶֽם׃
even all that Hashem has commanded you by Moses, from the day that Hashem gave commandment, and onward throughout your generations;
Rashi says
את כל אשר צוה וגו׳ – מגיד שכל המודה בעבודה זרה ככופר בכל התורה כולה ובכל מה שנתנבאו נביאים, שנאמר: למן
היום אשר צוה והלאה.
EVEN ALL THAT [Hashem] HAS COMMANDED [YOU] etc. – This tells us that he who acknowledges the divinity of an idol is like one who denies the Torah in its entirety and all that the prophets prophesied, because it states, "[and if you have erred and not done … all that the Hashem has commanded by Moshe] from the day that Hashem commanded (Moshe), and henceforth [throughout all your generations].
We have to understand - Already in the previous pasuk [כ"ב] it says
“When you shall err, and not observe all these commandments, which Hashem has spoken to Moshe."
The Sifrei expounds and is cited by Rashi that it is talking about Avoda Zara which is one mitzva but equal to all the mitzvos etc. [see there]. So we already have a teaching that Avoda Zara is like all the mitzvos so what was added in פסוק כ"ג?
Also, in פסוק כ"ב it says "אשר דבר ה' אל משה" whereas in פסוק כ"ג it says differently "את כל אשר צוה ה' אליכם מיד משה". [See the Ohr Hachaim].
We also have to understand the simple meaning of the words "מן היום אשר צוה ה' הלאה לדרתיכם". The Gemara in Horiyos [8b] expounds these words and Rashi here offers an explanation that doesn't seem to be the simple meaning of the pasuk. What is the SIMPLE STRAIGHTFORWARD meaning?
