Ninth of the Thirteen Principles of the Jewish Faith laid down by the Rambam in the twelfth century, and the fourth and last of the four principles relating to the Authority and Authenticity of the Torah, the nature of Prophecy, and the Prophecy of Moshe Rabbeinu, A”H:
“I believe with complete faith that this Torah will not be exchanged for another, nor will there be another Torah from the Creator, Blessed is His Name.”
The essence of this Principle is that in the Torah, its Written and Oral Components, the “Torah she-BiK’Tav” and the “Torah she-B’Al Peh,” respectively, G-d revealed to Man “all ye know on earth and all ye need to know,” to paraphrase John Keats who wrote in “Ode on a Grecian Urn” “Beauty is Truth; Truth, Beauty – That is all ye know on earth and all ye need to know.” Therefore, the Wisdom of the Torah is necessary and sufficient for Man to study in its great depth and, at the end, the greatest scholar will have tasted only a “drop from the sea.” This is true because the “Author” of the Torah used His infinite Wisdom in creating it.
Therefore, since we assume, as explicitly stated in the Eighth “Ani-Maamin” that “Torah min HaShamayim,” that the Torah was transmitted to Man from Heaven, and that took place on one cataclysmic occasion in history, the Revelation of G-d on Mt. Sinai, it follows that HaShem gave us all we need to know, if we spend our lifetimes working on it, and it has no need of augmentation by additional material or subtraction of any of its existing contents. Indeed, this Principle is stated explicitly in the Torah as a Negative Command: “You shall not add to the word that I command you, nor shall you subtract from it…” (Devarim (4:2)
Since we also trust HaShem that he does not “play games” with us, it follows that He gave us the exact Torah that we need, no more and no less, and that as Ben Bag-Bag says in Pirkei Avot (5:26), “Delve into it, and delve into it yet again, for everything is in it.”
The poetic rendering of this Principle in “Yigdal” is as follows:
“The Creator will never amend His Law, nor exchange it for another for all Eternity”.