Our Gemara on Amud Aleph uses an interesting idiom to describe Rav Yehuda's uncertainty about a halakha: "אִין וְלָא וְרַפְיָא בִּידֵיהּ" "Yes and no, and the matter was weak in his hands."

The idiom indicates a sense of flux, yes, no, back and forth. The choice of the Aramaic word "אין" "Iyn," which means "Yes," instead of the Aramaic word "Hen," which also means "yes," may just be a matter of dialect. However, Arvei Nachal (Nitzavim 2) sees it as a deliberately ambiguous word, which actually itself means both yes and no. In Aramaic, "Ayin" (naught) is spelled the exact same way. In that choice of word, an idea about the essence of knowing is being conveyed. To realize something new, is to let go of preconceptions and anchors, and to enter into confusion (even nothingness and void) until the newer conception falls into place.

The verses in Yechezkel about the Maase Merkava (1:14 and 22) describe a form of angels who "go to and fro" and have "the firmament above them," alluding to where the upper limits of the physical world meet up with the lower limits of the spiritual world. Specifically, the righteous person's soul can momentarily have enlightenment, piercing a certain veil of reality, but then hitting the limit and returning back to a lower state.

The structure of the morning prayer is deliberate. We first meditate on the heavenly bodies, including a recitation of the Kedusha performed by the angels of the Merkava to induce this fleeting awareness of a vast spiritiual Pleroma. This prepares us to properly accept the Yoke of Heaven in Shema with due dense of majesty and awe. This, in turn, sets the stage for a spiritual connection during shemoneh esre that Shulkan Arukh (OC 98:1) describes as possible to bring one to a "divestment of physicality" and "close to prophecy."

He says the understanding of what is real leads to a realization of the nothingness of the material world, and at that moment, everything dissolves in the face of the spiritual reality, which is not physical. Seeing into the nothingness (Ayin) brings a glimpse of the true everything (Iyn), which cannot be maintained in consciousness for but a moment. Yes and no, no and yes, back and forth.