God is one. Maimonides, Foundations of the Torah.

Hello.
We are studying the basics of Torah, and we wanted to ask if we understood correctly.
The Rambam explains: That something that is not a body is always one.
That the division is only on the part of the bodies and not on the essence of the matter.
We understood what he meant: For example, the concept of a triangle is one, and what belongs to two triangles is material that has a physical perception. For example, a pizza triangle and a triangle give way. But in the concept of a triangle, it is only one.
Therefore, there must be one spiritual essence.
It still remains to be clarified whether there is one essence that is the mother of all essences, that perhaps love is an essence separate from mercy, as we perceive it! And so in all essences? That is, God for every attribute. (Plural Elohim.)
And the answer: When each attribute has a different essence (God), we are obliged to say that there is a common essence for all of them, and that is that they are bound by reality (that they have existed since time immemorial).
And this is impossible: because different essences cannot be connected on the essential level unless there is another dimension that binds them together, such as matter that binds them to one place or one body. For example: the triangular essence, which is three sides, will never connect with the square one, which is four sides. Only on the physical level can a triangle be placed inside a square shape. But on the mental level there is no connection between them.
 
If so, it is also impossible to unite mercy with hatred, and mercy with the commitment to reality,
Therefore, we must assume that the essence of mercy is not an essence in itself, nor is the essence of the obligation of reality, but rather there is an essence that is unknown to us that unites within itself as one essence all essences and has one complete root!!! And in our world, the separation of essences into different definitions is created, so that mercy and suffering are perceived as different things.
I would like to know if we understood correctly.
And if not, then what does Maimonides mean, and do you think there is proof that God is one?
And if we were wrong, then how much we confused our minds. thanks.