Rav Achai:One who believes in a deity, different than the Holy One Blessed be He

[edu]

First a biography on Rav Achai from the Bar Ilan Responsa Project

SHEILTOT DE-RAV ACHAI
Rav Achai (Acha) of Shabcha was born ca. 680 CE and passed away in the land of Israel in 756. Even though he was one of the greatest Torah scholars of Babylonia, he was not appointed to the office of Ga'on. Rav Acha's Sheiltot is the first known halachic work composed in post-Talmudic times for public use. Written in Aramaic, it contains traditions which are unknown to us from other sources. Each sheilta deals with a particular halakhic theme, somehow associated with the weekly Torah reading, and containing a halakhic question, solution, and aggadic homilies. The Sheiltot was first published in Venice in 1546. Various commentaries were written on the work, including one by R. Naftali Tzvi Yehudah Berlin, the Netziv of Volozhin. A critical edition of the work was published between 1960 and 1977 by Professor S. K. Mirsky.

This is what Rav Achai has to say about a Jew who believes even in one deity, if that deity is not the Holy One Blessed be He.

שאילתות דרב אחאי פרשת יתרו שאילתא נב

שאילתא דאסר להון לדבי' ישר' למפלח לשום מדעם בעלמא ולאודויי אלא להקב"ה לחודיה שנאמר לא יהיה לך אלהים אחרים על פני וכתיב לא תשתחוה להם ולא תעבדם

Translation. In Rav Achai's commentary on the Decalogue in Parshat Yitro, Sheilta 52 he states:
It is forbidden for them of the House of Israel to serve anything in the world or admit to (alternate translation, offer thanks to) anything except the Holy One Blessed be He, exclusively. For it was stated, You shall not have other gods in my presence (or to be more literal, "upon my face"). And it is written, "Do not bow to them or worship them".

[edu]

It is a basic belief in Judaism that G-d does not have a body.
So why does the decalogue literally say, "upon my face".
It is basic belief in Judaism, that those types of passages in the Bible are symbolic and not meant to be taken literally. Just like when the magicians of Pharaoh saw the plague of lice and said "it is the finger of the L-rd".
Not that G-d literally has fingers made out of lice, but rather just like the actions done by someone's finger is a small indication of his true power, so too, the plague of lice was a small indication of G-d's power.