”The Jews … to this day … still assert that God is only one in person, as well as in nature.”
(William Beveridge, Private Thoughts on Religion, p. 66)
And that He (God) alone is the proper recipient of prayer.
The "one Lord" (YHWH) cannot be differentiated from prayer which He alone is to receive.
The underlined below is mine:
Judaism 101: The Shema can also be translated as "The L-rd is our G-d, The L-rd alone," meaning that no other is our G-d, and we should not pray to another. (The Nature of G-d)
http://www.jewfaq.org/g-d.htm