I've found this article which quoted some interesting thoughts:
Our sages said about the verse (Shabbat 105b), “There shall not be a strange god within you, nor will you bow before a strange god.”
What is the strange god in man’s body? It is the evil inclination. This means that an idol-worshipper is called “the evil inclination.” It follows that when speaking of a single body, then idol-worshipping, which is called “a foreign god” or “a strange god,” is entirely within man.
So here are my questions: Why is the evil inclination compared to a foreign/strange god?
Also, what is the connection between idolatry and the evil inclination?
And why is it assumed that both come from or occur within man?