This great verse has been recited countless times by Israelites down through the centuries, setting forth their distinctive belief in one great Creator God. The Jews had retained their original belief in creation, handed down from Noah, while the other nations had all allowed their original monotheistic creationism to degenerate into a wide variety of religions, all basically equivalent to the polytheistic evolutionism of the early Sumerians at Babel.
But along with its strong assertion of monotheism, there is also a very real suggestion that this declaration, with its thrice-named subject, is also setting forth the Triune God. The name, "Lord," of course, is Yahweh, or Jehovah, the self-existing One who reveals Himself, while "God" is Elohim, the powerful Creator/Ruler. "Jehovah our Elohim is one Jehovah" is the proclamation. A number of respected Jewish commentators have acknowledged that the verse spoke of a "unified oneness," rather than an "absolute oneness." The revered book called the Zohar, for example, even said that the first mention was of the Father; the second one the Messiah; and the third, the Holy Spirit.
The key word "one" (Hebrew, achad) is often used to denote unity in diversity. For example, when Eve was united to Adam in marriage, they were said to be "one flesh" (Genesis 2:24). Similarly, on the third day of creation, the waters were "gathered together unto one place," yet this gathering together was called "Seas" (i.e., more than one sea; Genesis 1:9-10).
Thus, Israel's great declaration should really be understood as saying in effect: "The eternally omnipresent Father, also Creator and Sustainer of all things, is our unified self-revealing Lord." HMM http://www.icr.org/article/5896/