The Introduction, which is formally part of ‘Part I’, is a striaghtforward account of Maimonides’ reasons for writing this book. Addressed to a promising young pupil, Maimonides states:

The object of this treatise is to enlighten a religious man who has been trained to believe in the truth of our holy Law, who conscientiously fulfills his moral and religious duries, and at the same time has been successful in his philosophical studies. Human reason has attracted him to abide within its sphere; and he finds it difficult to accept as correct the teaching based on the literal interpretation of the Law … . Hence he is lost in perplexity and anxiety. If he be guided solely by reason, and renounce his previous views which are based on those [i.e., literal] expressions, he would consider that he had rejected the fundamental principles of the Law; and even if he retains the opinions which were derived from those expressions, and if, instead of following his reason, he abandon its guidance altogether, it would still appear that his religious convictions had suffered loss and injury.

This passage shows that Maimonides is concerned primarily with the relationship between ‘philosophy’ and the ‘Law’. He goes on to identify the expression Ma’ase Bereshit (account of the creation, from Genesis 1) with ‘Natural Science’, and the expression Ma’aseh Mercabah (description of the Chariot, from Ezekiel 1) with ‘Metaphysics’. At this stage, Maimonides reminds the reader of the Talmudic rule that ‘One may not expound … upon Genesis 1 in front of two students, and upon Ezekiel 1 in front of even one, unless he is wise and already understands it on his own.’ (Mishnah Hagiga 2:1)

The body of Ma’aseh Mercabah literature arose out of the rabbinical analysis of esoteric visions of the supernatural. The prototypical account is explicated in Ezekiel 1: Ezekiel sees an eldritch chariot comprised of incomprehensible beings, as well as a representation of the divine Presence. This narrative lends the genre its name, Ma’aseh Mercabah, which translates to “work of the Chariot.” (source).

The sages have repeatedly discouraged the public from studying Ma’aseh Mercabah. Ecclesiasticus 3:22 commands:

Seek not the things that are too high for thee, and search not into things above thy ability: but the things that God hath commanded thee, think on them always, and in many of his works be not curious.

The Talmud (Chagigah 13a) interprets this admonition as pertaining to Ma’aseh Mercabah:

The Gemara comments: Until here, you have permission to speak; from this point forward you do not have permission to speak, as it is written in the book of Ben Sira: Seek not things concealed from you, nor search those hidden from you. Reflect on that which is permitted to you; you have no business with secret matters. It is taught in a baraita: Rabban Yoḥanan ben Zakkai said: What response did the Divine Voice provide to that wicked man, Nebuchadnezzar, when he said: “I will ascend above the heights of the clouds; I will be like the Most High” (Isaiah 14:14), thereby intending to rise to heaven? A Divine Voice came and said to him: Wicked man, son of a wicked man, descendant, i.e., follower of the ways, of Nimrod the wicked, who caused the entire world to rebel against Him during the time of his reign. […] It is taught in the mishna, according to the Gemara’s explanation: Nor may one expound the Design of the Divine Chariot to an individual. Rabbi Ḥiyya taught: But one may transmit to him, an individual, the outlines of this topic, leaving him to comprehend the rest on his own.

In light of these matters, Maimonides states:

The Ma‘aseh Mercabah must not be fully expounded even in the presence of a single student, unless he be wise and able to reason for himself, and even then you should merely acquaint him with the heads of the different sections of the subject. (Babyl. Talm. Ḥagigah, fol. II b). You must, therefore, not expect from me more than such heads. And even these have not been methodically and systematically arranged in this work, but have been, on the contrary, scattered, and are interspersed with other topics which we shall have occasion to explain. My object in adopting this arrangement is that the truths should be at one time apparent, and at another time concealed. Thus we shall not be in opposition to the Divine Will (from which it is wrong to deviate) which has withheld from the multitude the truths required for the knowledge of God, according to the words, “The secret of the Lord is with them that fear Him” (Ps. 25:14).

Similar interdictions were issued regarding Ma’aseh Bereshit, which comprises certain mystical topics associated with the Genesis creation account. For example, the Talmud (Chagigah 11b) says:

One may not expound the topic of forbidden sexual relations before three or more individuals; nor may one expound the act of Creation and the secrets of the beginning of the world before two or more individuals; nor may one expound by oneself the Design of the Divine Chariot, a mystical teaching with regard to the ways God conducts the world, unless he is wise and understands most matters on his own.

As a result, Maimonides continues:

Know that also in Natural Science there are topics which are not to be fully explained. Our Sages laid down the rule, “The Ma‘aseh Bereshith must not be expounded in the presence of two.” If an author were to explain these principles in writing, it would be equal to expounding them unto thousands of men. For this reason the prophets treat these subjects in figures, and our Sages, imitating the method of Scripture, speak of them in metaphors and allegories; because there is a close affinity between these subjects and metaphysics, and indeed they form part of its mysteries.

In this fashion, Maimonides claims that some truths of Natural Science and Metaphysics are hidden within his work. What Maimonides meant by this sort of claim has created some debate in modern scholarship.

Maimonides notes that certain passages in the Talmud (Midrash) “appear to be inconsistent with truth and common sense”, but that if

an ill-informed Theologian reads these Midrashim, he will find no difficulty; for possessing no knowledge of the properties of things, he will not reject statemtents which involved impossibilities. When, however, a person who is both religious and well educated reads them, he cannot escape the following dilemma: either he takes them literally, and questions the abilities of the author and the soundness of his mind…

Maimonides states that the material to come has, in fact, been passed down the generations as part of the religious tradition of Judaism, and does not take credit for coming up with something entirely new. However, what is new is his effort to write these things down, an activity about which he is quite conflicted because of the Talmudic dictum to never discuss these subjects in front of lay people, and to take great care even when discussing them with specialized students. He says that the contents of this book include “topics which, since the time of our captivity have not been treated by any of our scholars as far as we possess their writings”. He expounds further on this subject in the first few paragraphs of GP.I.71.