Paraphrased loosley from the Artscroll Siddur: The recitation of The Shema represents your acceptance of YHWH's absolute authority and sovereignty. By declaring that Elohim is One, Unique, and Indivisible, we submit our lives to His will.
The Shema contains many passages of scripture found in the Bible, specifically in the Torah, the 1st five books of the Bible. The Shema prayer starts off with a declaration: "Hear O Israel, YHWH our Elohim, YHWH is One! (Deu 6:4). In the gospels, Our Messiah, Yahshua of Nazareth was asked what is the first commandment of all? Yahshua responded by quoting three scriptures found in the Torah (1st five books of instruction YHWH gave to Moshe to give to the children of Israel) in Mark 12:29-31 Yahshua said: "...the first is Hear, O Israel; The L-rd our G-d, the L-rd is one:" -(This comes right out of Deuteronomy 6:4). Yahshua proceeds in Mark 12:30 with "and you shall love the L-rd your G-d with all your heart, and with all your soul, and with all your mind, and with all your strength." -(This also comes right out of the Torah: Deut 6:5-9). Yahshua in Mark 12:31 finishes with "The second is this, you shall love your neighbor as yourself. There is no other commandment greater than these." -(This also comes out of the Torah: Leviticus 19:18). So we see Messiah Yahshua quoting back scripture (Torah) to the scribe's question.
The Shema consists of a combination of scripture from Deuteronomy 6:4-9, Numbers 11:13-21, Numbers 15:37-41. These three passages of scripture define the following:
(1) Deut 6:4-9 = Acceptance of the instructions to love Elohim
(2) Numbers 11:13-21 = Acceptance of Elohim's instructions and the concept of reward and punishment
(3) Numbers 15:37-41 = Acceptance of the Exodus account that Elohim brought out the children of Israel (our ancestors) from Egypt and to remember and perform all of Elohim's instructions as defined in His Torah.
It is important that (when outside the country of Israel) one face Israel when reciting the "Shema" and when "In Israel" to face Jerusalem. If you are in Jerusalem, it is important to face the Temple mount where the Temple once stood. It is NOT a commandment but in scripture it is recorded:
1 Kings 8:30 "And listen to the supplication of your servant and your people Israel, when they pray toward this place; hear in heaven Your dwelling place; hear and forgive."
This prayer was from Solomon after the 1st Temple was built and dedicated to YHWH. I encourage you to read all of 1 Kings 8 & 9 to get a feel for this amazing event in the history of Israel!