Negative commandment · Lo Ta’aseh #1 of 613
Not to consider the thought that there is another divinity aside from G-d
שלא לעלות במחשבה שיש שם אלוה זולתי ה'
The verse · Shemot 20:3
לֹא־יִהְיֶה־לְךָ אֱלֹהִים אֲחֵרִים עַל־פָּנַָי
“Thou shalt have no other gods beside me.”
The Rambam’s words
The first mitzvah of the negative commandments is not to consider the thought that there is another divinity aside from G-d, as [Exodus 20:3] states: "You shall have no other gods before Me."
מצוה ראשונה ממצוות לא תעשה, שלא לעלות במחשבה שיש שם אלוה זולתי ה', שנאמר "לא יהיה לך אלוהים אחרים, על פניי" (שמות כ,ב; דברים ה,ו).
Why · Sefer HaChinuch #26
That we not believe in a god besides Hashem alone
“The root of this commandment is revealed and known.”
Who & when
“And [it] is practiced by males and females in every place and at all times.”
Where in the Mishneh Torah
Hilchot Foundations of the Torah הלכות יסודי התורה