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.