“Those who believe that G-d is One, and [also believe] that He has many attributes, declare the [Divine] unity with their lips and assume plurality [i.e. many gods] in their hearts.” 
The Rambam — Maimonides — was making a philosophical point above about the futility of describing or defining G-d by positive statements or “attributes,” because of the linguistic pitfalls that are opened up by doing so. He staunchly believed that G-d could only be defined “negatively” — by what G-d is not.
“Given 613 original commandments, [Maimonides] argues that all are means to the fulfillment of the first two [of the “10 Commandments” given to Mosheh at Mt. Sinai], which he interprets as belief in the existence of G-d and rejection of idolatry.  Together these commandments make up what we call monotheism. From Maimonides’ perspective, however, there is more to monotheism than belief in a single deity. To satisfy the first two commandments, one must believe in a timeless, changeless, immaterial deity who is one in every respect and unlike anything in the created order. A person who fails to recognize such a deity is accorded the status of an idolater no matter how many other commandments [he or] she may fulfill or how fervently [he or] she may fulfill them. Simply put, to worship G-d under a false description is not to worship G-d at all.” 
Parenthetically, he was also making a secondary point: We need to examine our own assumptions. It’s possible to declare G-d’s Oneness via the “Shema” scrupulously in every required prayer-service, and yet still have unexamined assumptions which, in fact, make our actual belief closer to polytheism — i.e. a belief in multiple gods.
How can this be?
Let’s imagine that you win the lottery. Many people thank G-d.
Now, let’s imagine that you’re walking home from picking up your lottery winnings; while you’re walking, the person in front of you attempts to throw some paper into a public trash basket, but a sudden gust of wind carries the paper off and it hits you in the face! Do you say, “Thank G-d?” Of course not. This had nothing to do with G-d. It was just an accident, right? But at that moment, you’ve affirmed your belief in a power other than G-d; the power of “accident.” One might even say that this power is another god that you recognize, named “Accident.”
You keep walking. The wind dies down. Suddenly, you see a $100 bill at your feet. Do you say, “Thank G-d?” Probably not. This had nothing to do with G-d. This was just a bit of good luck, right? But then, you’ve affirmed belief in a third power; the power of “luck.” This is another god, named “Luck.” (Perhaps, in this theology, “Luck” is the sister or brother of “Accident.”)
Now, you’re back at home. You live on the 5th floor of an apartment building. You walk into your kitchen and see that the trash has to be emptied. Would you throw it out of the window? No, of course not. Environmental and sanitary concerns (and legal consequences) aside, it might hit someone down on the street, right? But then — you’re affirming your belief in “Accident” again. You’re also affirming belief in the immutable power of gravity; whatever goes up (or out the window) must come down. G-d has nothing to do with that, right? Again — being an immutable power (or “law”) not dependent on G-d, it’s like a god named “Gravity.”
In each example, we’ve attributed an event to something other than G-d.
Any “power” other than G-d is another god!
The Talmud characterizes “monotheism” in part as a belief that G-d, and only G-d, is the cause of every event, regardless of how seemingly insignificant: e.g. “…one…puts his hand in his pocket intending to pull up three coins and pulls up two…” 
“…trusting in Ha-Shem is…the belief that nothing happens by chance, and that everything that happens under the sun is the result of a decree by the Almighty…” 
This, of course, runs contrary to the model that physics (and science, in a broader sense) would seem to mandate.
Without negating the benefit of scientific inquiry, we must also acknowledge that science itself can be working within the limitations of what it understands. Think of the effect of Einstein’s work on the understanding provided by Newtonian Physics.
In its view of ultimate causality, could Torah be suggesting a paradigm that is more advanced than science, rather than one that is more primitive?
 Maimonides; Guide for the Perplexed; ch. 50 (Dover Publications; p. 67)
 In Judaism, the first commandment is: “I am the Lord thy G-d,” which Maimonides (MT 1, Principles of the Torah, 1.1–7) takes as an affirmative precept mandating belief in the existence of G-d.
 Arachin 16b
 Chazon Ish (Rabbi Avraham Yeshayahu Karelitz); Faith and Trust (Emunah u-Bitachon); ch. 2, sec. 1; Yakov Goldstein, trans.; p. 38-40