What do you think of this quote from a rabbinical (albeit mystic) source based on his 2nd century writings?
240. The daily profession of unity is a meditation for the sake of knowledge and for paying attention. We have explained this meditation in many places. The daily meditation is the profession of unity in the verse, "Hear, O Yisrael (Sh'ma Yisrael), Hashem our Elohim; Hashem is One." And they are all one. Therefore He is called One. HE ASKS: There are three names here, so how are they one? We proclaim One, NAMELY "HEAR O YISRAEL, HASHEM OUR ELOHIM; HASHEM IS ONE," yet how can they be one?
241. This is made known through the vision of the Holy Spirit. They become part of the mystery of the mirror of the closed eye, to make known that the three COLUMNS ALLUDED TO IN "HASHEM OUR ELOHIM, HASHEM" are one, and this is the secret of the audible sound. Sound is one, and has three aspects - fire, air and water - which are all one in the secret of the sound. Also here, "Hashem, our Elohim; Hashem" are one. They are three aspects but are one.