[The regulations governing] release from vows hover in the air and have no [firm Scriptural] support. [Certain] laws of the Sabbath, chagigah, and me'ilah are like mountains suspended by a hair, for there are few Scriptural references and many laws. [The regulations governing] property law, the [sacrificial] services, purity and contamination, and illicit relationships have [firm Scriptural] support. All of these are essentials of the Torah.

We may expound neither on [the subject of] illicit relationships to [a group of] three, nor on the account of the Creation to [a group of] two, nor on [the account of] the Merkavah to an individual unless he is wise and understanding through his own knowledge.  Whoever speculates on four things, it would be better for him had he not come into the world: What is above, what is below, what was before, and what will be after.  Similarly, whoever has no regard for the honor of his Maker, it would be better for him had he not come into the world.