The essential "Shema" is stated in Deuteronomy 6:4: SHEMA YISRAEL!, YHWH ELOHEINU, YHWH ECHAD.
Translated literally to English, this is: LISTEN YISRAEL!, YHWH GOD, YHWH ONE.
The name Yhwh is a variation on "Ahyh" ("I am" in English). In Exodus 3:14, after Moses inquires about God's name, God says to Moses that His name is "I am who I am", or in Hebrew "Ahyh ashr ahyh" ("אהיה אשר אהיה"), and then God says "You shall say this to the children of Israel: 'I am' ['Ahyh'] has sent me to you." Immediately after this, in Exodus 6:15, we read "And God said further to Moses: 'You shall say this to the children of Yisrael: Yhwh, your father's God, Abraham's God, Isaac's God, and Jacob's God has sent me to you. This is my name forever, and this is how I am to be remembered for generation after generation."
In summary, even though God first commands to be introduced to the Israelites as "Ahyh"/"I am", God also immediately commands that the Israelites shall thereafter referr to him as "Yhwh".
Translation note: Most (but not all) translations of the Hebrew Torah text typically replace the Hebrew characters for "Yhwh" with "Lord" (or sometimes "Adonai" is used, which is the literal Hebrew word for "Lord") or, alternatively, with "TheName" ("HaShem" in Hebrew) or "G-d"/"Elohim". This practice is intended as a sign of respect by the translator. It arises from Rabbinical Judaism but has also found its way into most "Old Testament" translations used in Christianity. In Rabbinical Judaism, the practice is specifically to avoid speaking outloud the sacred proper name of God, hence replacing it with "Lord"/"Adonai" or "TheName"/"HaShem" or "G-d"/"Elohim". In this website we will typically not replace any words from the Torah because we believe it is not for us to add or subtract to it. Furthemore as we can see in the quote from Exodus 6:15, above, we (the descendants of Israel, to whom this Sinai Law is addressed) are actually commanded to use it: "AND THIS IS HOW I AM TO BE REMEMBERED FOR GENERATION AFTER GENERATION." One additional point regarding God's name: Because the Sinai covenant is between God and Israel, the requirement to remember God by the name Yhwh is not addressed to nations other than Israel. Hence, the Torah is not forbidding other nations (i.e. Gentiles) to address God in their own language and according to their own designation (as long as they acknowledge that it is intended to denote the One-and-Only God, Creator of all Existence). Having said that, there are no other proper names in use today by any other nations or religions who also acknowledge a One-and-Only God. For example the word "Allah" in Arabic and Islam in general is not a proper name. Rather, "Allah" is simply the Arabic word for "God", just like "Elah" is the Aramaic word for "God" and "Dios" is the Spanish word for "God".
The meaning of "Yhwh":
Where as "I am"/"Ahyh" is in first person, "Yhwh" is third person and best translated as "He Is" or "He Causes To Be" or "He who causes existence". The Hebrew word Yhwh is masculine, third person, and it is a verb.
A note on Anthropomorphisms:
Although the name "Yhwh" utilizes masculine Hebrew to refer to God, the Shema of Deuteronomy 6:4 reminds us not only that God is One, but that "One" is the only attribute assignable to God. Furthermore, even the context of the word "One" is not numerical (after God created numbers too, and therefore transcends numbers too). Rather, the context of "God is One" is in the sense of "God is Unique" or "God is One Alone (i.e. not accompanied by anything else)". The concept expressed in the Shema is understood by Israel to supercede all language usage in the Torah where inevitably God is referred to using attributes (e.g. masculine as in "Yhwh"/"He Creates", or plurality as in "Elohim", or "Angry" or "Merciful", etc.). Stressing this point, there are repeated injunctions in the Torah where Israel is forbidden to describe or depict God in any manner whatsoever. For example:
Deuteronomy 4:25-26, When you have had children and children's children, and become complacent in the land, IF YOU ACT CORRUPTLY BY MAKING AN IDOL IN THE FORM OF ANYTHING, thus doing what is evil in the sight of the Lord your God, and provoking him to anger, I call heaven and earth to witness against you today that you will soon utterly perish from the land that you are crossing the Jordan to occupy; you will not live long on it, but will be utterly destroyed.
Deuteronomy 4:15-19, Since you saw no form when the Lord spoke to you at Horeb out of the fire, take care and watch yourselves closely, so that you do not act corruptly by making an idol for youselves, in the form of ANY figure - the likeness of male or female, the likeness of any animal that is on the earth, the likeness of any winged bird that flies in the air, the likeness of anything that creeps on the ground, the likeness of any fish that is in the water under the earth. And when you look to the heavens and see the sun, the moon, and the stars, all the host of heaven, do not be led astray and bow down to them and serve them...
Deuteronomy 5:8, You shall not make for yourself an idol, whether in the form of anything that is in heaven above, or that is on the earth beneath, or that is in the water under the earth.
Coupled with the above injunctions against depicting God in any way, the Shema gives us the essential statement of monotheism in human culture. It is the concept that humanity is all under a single God. This God is beyond description and humans are not allowed to create their own depictions ("idols") of this One God. Traditionally, nations would create their own depictions of God (or gods) and these depictions evolved into tribal gods that we used to justify war against other peoples and their "foreign gods". By forbidding the use of idols and focusing on ECHAD as the only attribute of God, the Torah is providing the formula for a single humanity, united under the single God. Hence we find here not only the essential statement of monotheism, but also the implicit formula for ethical monotheism. With Leviticus 19:18 ("Love your neighbor as yourself") we then have the Torah as the explicit teaching of ethical monotheism.
The full Shema is comprised of 3 paragraphs from the Torah : Deuteronomy 6:4-9, Deuteronomy 11:13-21, and Numbers 15:37-41. The scripture text quoted below is from "Commentary on the Torah with a new English translation and the Hebrew text" by Richard Friedman, Harper-Collins, 2001.
Deuteronomy 6:4-9 : Shema (LISTEN), Yisrael: Yhwh is our God. Yhwh is echad (one/alone). And you shall love Yhwh, your God, with all your heart and with all your soul and with all your might. And these words that I command you shall be on your heart. And you shall impart them to your children, and you shall speak about them when you sit in your house and when you go in the road and when you lie down and when you get up. And you shall bind them for a sign on your hand, and they shall become bands between your eyes. And you shall write them on the doorposts of your house and in your gates.
Deuteronomy 11:13-21 : So it will be, if you will LISTEN to my commandments that I command you today, to love Yhwh, your God, and to serve Him with all your heart and with all your soul, then I'll give your land's showers at their time, early rain and late rain, and you'll gather your grain and your wine and your oil. And I'll give vegetation in your field for your animals, and you will eat and be full. Watch yourselves in case your heart will be deceived so you'll turn and serve other gods and bow to them, and YHWH's anger will flare at you, and He'll hold back the skies, and there won't be showers, and the earth won't give its crop, and you'll perish quickly from the good land that Yhwh is giving you. So you shall set these words of mine on your heart and on your soul, and you shall bind them for a sign on your hand, and they shall become bands between your eyes, and you shall teach them to your children, to speak about them when you sit in your house and when you go in the road and when you lie down and when you get up, and you shall write them on the doorposts of your house and in your gates, so that your days and your children's days will be many on the land that Yhwh swore to your fathers to give them, like the days of the skies over the earth.
Numbers 15:37-41 : And Yhwh said to Moses, saying, "Speak to the children of Yisrael, and you shall say to them that they shall make fringe on the corners of their clothes through their generations. And they shall put a blue string on the fringe so you will see it and bring to mind all of Yhwh's commandments and will do them, and you will not go around after your heart and after your eyes, because you whore after them. So you will bring to mind and do all my commandments, and you will be holy to your God. I am Yhwh, your God, who brought you out from the land of Egypt to be God to you. I am Yhwh, your God.
Implications of the Shema:
In a polytheistic world vision there are many gods. What is the Shema telling us that makes it such a revolutionary statement? Let's take the example of the Graeco-Roman worldview. In such a worldview, there are many deities, each of which constitutes its own power in the universe. Some are more powerful than others, yet they are all independent and can act on their own. Now let's look at the Shema and the Torah's worldview. Are there no supernatural beings also in the Hebrew Bible? There certainly are, since we hear about angels and the great power that they can wield. Is this not then polytheism in the same way as the Greek pantheon, with one very powerful Zeus and many lower level powers/divinities ? No, it is not, for the following reason: The Shema is telling us that there is one source of all existence in the world. "YHWH ECHAD" means "HE THAT CAUSES EXISTENCE IS ONE/ALONE". All existence, all events in the world are caused to exist by Yhwh ONLY. Angels may be supernatural in the sense that they usually operate on a different plane of existence (lets say, something like 'another dimension') and they have superior technology than humans, however the Shema is telling us that at the end of the day, all the powers that we see in the universe, whether angelic, human, or anything in nature, are the result of Yhwh. The world is a deterministic world, not a world of independent powers, each with its own will. To us, events in the world may seem to appear to us like non-deterministic. Let's say that today I go into the office and all things go as we expected; But then tomorrow something unexpected happens: I am let go from my job. What happened ? Bad Luck? Some decision maker made a decision that had not been previously in the works? No. The unexpected event seems like the independent will of some agent (in this case my boss) but in reality it is only our limited perception of reality that causes us to be surprised. The event, as all events in the world, emanates from God's design (perhaps figured out already at the beginning of time) and is certainly not a surprise to God. All events, 'good' and 'evil' emanate from one source: "HE THAT CAUSES EXISTENCE".
Another revolutionary implication of the Shema is that of one humanity. In the polytheistic world view, each nation had a creation story in which a particular deity has favored that nation's creation against the adversity of its enemies. And therefore each nation believed in tribal gods, which could be dressed up in local trappings and given a local name. In other words, the local deities functioned as a type of supernatural king, protecting the nation and assisting it against it enemies. In fact even much of the early conception of God by the Israelites is that of a tribal God; a God that choose Israel among all nations and helps Israel against its enemies. However, over time the vision changed. The Shema tells us that there is one God for one tribe: humankind. Yes, Israel may be chosen, but it is chosen for a specific purpose, not chosen in the sense of being the only one accepted to persist in human history or salvation. So then, the Shema, by eliminating the possibility of tribal gods, becomes the great unifier of humanity. One Power means One Power for ALL nations, One Power for all humanity.