“Rabbi Natan says, ‘When he laughs he says, ‘Tighten well, tighten well, for the voice is good for perfumes.’’”
“Perfumes” means a scent that ascends from below upward. This is the quality of Hochma [wisdom] that is received in Atzilut specifically in this order. But when receiving Hochma from above downward, it is regarded as GAR, and there is no room for Hassadim [mercies] there, and Hochma without Hassadim does not shine. It follows that “perfumes” are regarded as Hochma.
See in The Zohar and in the Sulam [Ladder commentary on The Zohar] that “voice” is called Hassadim. This is the meaning of saying that when he had to extend Hochma when it is included in Hassadim, he says “Tighten well, tighten well,” meaning not to receive the Hochma only in narrowness, which is VAK, illumination from below upward, so there will be room to extend Hassadim, which is called “voice.”
This is so because “The voice is good for perfumes,” meaning that Hassadim is good for Hochma because Hochma without Hassadim cannot shine.