Maimonides, answered from the texts and cited to the page.
The foundation from which all thirteen principles grow is stated at the head of Mishneh Torah: the foundation of all foundations and the pillar of wisdom is to know that there is a Primary Being who brought into being all existence.1 From that single sentence the architecture follows necessarily. The first principle is the existence of this Primary Being — that He exists, and that His existence is not like the existence of anything else.
All the beings of the heavens, the earth, and what is between them came into existence only from the truth of His being.2 Were one to imagine that He does not exist, no other being could possibly exist.3 Were one to imagine that none of the other entities exist, He alone would continue to exist, and the nullification of their existence would not nullify His.4
His truth, therefore, does not resemble the truth of any of their beings.5 The second principle is His unity — that this Primary Being is one, not one of a genus or species, not one as a body is one, but uniquely, absolutely one. The third is His incorporeality — that He has no body and no force within a body, and every verse of Scripture that speaks of His hand or eye or anger must be read as the Torah speaking in the language of man.
The fourth is His eternity — that He preceded all things and will outlast all things. The fifth is that He alone is worthy of worship and that directing worship toward any other being is forbidden. The sixth is prophecy — that God inspires men with the prophetic gift when the conditions of intellectual and moral perfection are met. The seventh is the supremacy of the prophecy of Moses, which was of an entirely different kind from all others, without intermediary, without the imaginative faculty, face to face.
The eighth is that the Torah now in our hands is the Torah given to Moses at Sinai. The ninth is that the Torah is immutable and will not be replaced. The tenth is divine omniscience — that He knows the acts of men and does not avert His attention. The eleventh is reward and punishment — that He rewards those who observe the commandments and punishes those who transgress them.
The twelfth is the coming of the Messiah — that one must await him even if he tarries. The thirteenth is the resurrection of the dead. I formulated these principles in the introduction to chapter ten of Sanhedrin — what is called Pereq Heleq — precisely because I had concluded that it was necessary to elucidate religious fundamentals in my works on law, preferring to have the truths accepted by the masses rather than presented in the idiom of philosophical inquiry alone.6
I wished all of this established on religious dogmas, so that those called disciples of the wise would build their legal details on legal foundations, and would no longer cast the knowledge of God behind their backs, but would exert themselves to the limit of their power to attain what will perfect them and bring them nearer to their Creator.7
The foundation of all foundations and the pillar of wisdom is to know that there is a Primary Being who brought into being all existence.Mishneh Torah, Foundations of the Torah
All the beings of the heavens, the earth, and what is between them came into existence only from the truth of His being.Mishneh Torah, Foundations of the Torah
If one would imagine that He does not exist, no other being could possibly exist.Mishneh Torah, Foundations of the Torah
If one would imagine that none of the entities aside from Him exist, He alone would continue to exist, and the nullification of their [existence] would not nullify His existence.Mishneh Torah, Foundations of the Torah
Therefore, the truth of His [being] does not resemble the truth of any of their [beings].Mishneh Torah, Foundations of the Torah
More than anything else I preferred to have the truths accepted by the masses. I therefore published principles that need to be acknowledged in the introduction to the commentary on the Mishnah regarding prophecy and the roots of tradition and what every Rabbanite had to believe concerning the Oral Law. In chapter 10 of Sanhedrin I expounded fundamentals connected with the beginning and the end.Epistles, pp. 60–61
I wish to have all this established on religious dogmas. They will no longer cast the knowledge of God behind their backs, but will exert themselves to the limit of their power to attain what will perfect them and bring them nearer to their Creator.Epistles, pp. 60–61