4. God's Unity
Yesodei HaTorah 1:7
God is One. He is not two or more. He is also One in a way that is different from everything else: He is not part of a larger category that includes many individual things, nor can he be divided into different parts like a person can. He is completely One in a manner totally unique to Him.
If there were more than one “god,” they would have to have bodies because that’s how similar beings are separated from one another. If God were to have a body, He would be limited because that’s exactly what a body is: a limitation. And any being that is limited can only possess limited power. Since God has unlimited power, as discussed above, we can easily infer that His power must not be the power of a body. Since God does not have a body, the limitations associated with having a body do not apply to Him. Perforce, God must only be One.
Knowing that God is One fulfills a Torah obligation: “Listen, Israel: Hashem is our God; Hashem is One” (Deuteronomy 6:4).
Yesodei HaTorah 1:8
The Torah and Navi (Books of the Prophets) tell us explicitly that God does not have a body. Deuteronomy 4:39 says, "Because Hashem, your God, is God in the heavens above and on the earth below" and a body cannot be in two places at the same time. Similarly, Deuteronomy 4:15 says "you did not see any image" (at Sinai), and Isaiah 40:25 says, "To whom can you compare Me, with whom I will be equal?" If God were limited by a body, He would in fact be like other bodies.