There are some subjects which are so delicate, and so open to misunderstanding, that they should only be taught in very small groups. Specifically, we are taught in Mishna Chagigah 2:1 in today’s daf (Chagigah 11b) that a Torah teacher should not attempt to explain the laws of forbidden relationships (עריות) that are not explicitly stated in the Torah and which require exegesis to derive their details before a crowd of three or more students (i.e. they may do so if teaching one or two students). Moreover, they should not attempt to share exegetical insights relating to the manner in which the world was created (מעשה בראשית) before two or more students (i.e. they may do so if teaching a student one-to-one). And moreover, they should not attempt to share exegetical insights relating to the Divine Chariot (מרכבה) to any individual student unless that student was (אלא אם כן היה) wise and can derive matters on their own having been taught the foundation of a subject.
You will note that the Mishna uses an unexpected word. Rather than stating that the מרכבה can be taught to a student who ‘is’ wise (אלא אם כן הוא חכם), it states that it can be taught to a student who ‘was’ wise (אלא אם כן היה חכם). Addressing this point, Rav Yosef Chaim explains (in his ‘Ben Yehoyada’) that a teacher should not begin their teaching of a student with mystical subjects such as the Divine Chariot (מרכבה). Instead, a student who wishes to learn this should have already studied a substantial amount of non-mystical content from their teacher, and as a result of the teacher being satisfied with the wisdom of their student (i.e. they know that the student ‘was’ wise), they can then make the decision to teach them about the Divine Chariot (מרכבה).
From here we learn a number of important lessons: Firstly, that the authentic study of Jewish mysticism only occurs when studying directly from a teacher (which is why Jewish mysticism is called קבלה – meaning the act of directly ‘receiving’ wisdom from a teacher). Secondly, that it can only begin once a student has achieved a full understanding of the core Jewish teachings and texts (eg. Tanach, Mishna, Gemara). And finally, that such study can only begin once a student has demonstrated the Torah thinking skills to independently derive authentic conclusions having first been taught the foundation of a given Torah subject.