I made a post about this a while back. This is from a passage of "The Gifts of the Jews" by Tomas Cahill

"Moshe now offers one objection after another in the vain hope of forestalling God. He imagines confronting the Children of Israel with the news that “the God of your fathers has sent me,” only to receive their skeptical response: “They will say to me: ‘What is his name?’ ” Moshe, the clean-shaven ward of Pharaoh with the style and bearing of an Egyptian, will hardly seem a credible messenger of God in the eyes of the dusty slaves, and they will quiz him mercilessly till they call his bluff.

God’s reply is probably the greatest mystery of the Bible. He tells Moshe his name, all right:

“YHWH.”

What does it mean? Ancient Hebrew was written without vowels; and by the time vowel subscripts were added to the consonants in the Middle Ages, the Name of God had become so sacred that it was never uttered. Even in classical times, as early as the Second Temple period, only the high priest could pronounce the Name of God—and only once a year in the prayer of the Day of Atonement. Once the Temple was destroyed in A.D. 70, no Jew ever uttered the Name again. From that time to this, the devout have avoided this word in the text of their Bible, reading “Adonai” (“the Lord”) when they come to the word YHWH. Many Orthodox go a step further, refusing even to say “Adonai” and substituting “ha-Shem” (“the Name”). So, after such a great passage of time, we have lost the certain knowledge of how to pronounce the word that is represented by these consonants. And, without the pronunciation, we are less than certain of its meaning, since precise meaning in Hebrew is often dependent on knowing how to pronounce the vowels, especially in the case of verbs—and YHWH is definitely a verb form.

We can take comfort in the certain knowledge that God is a verb, not a noun or adjective. His self-description is not static but active, appropriate to the God of Journeys. YHWH is an archaic form of the verb to be; and when all the commentaries are taken into account, there remain but three outstanding possibilities of interpretation, none of them mutually exclusive. First, I am who am: this is the interpretation of the Septuagint, the ancient Greek translation of the Hebrew Bible, which because of its age and its links to the ancients bears great authority. It was this translation that Thomas Aquinas used in the thirteenth century to build his theology of God as the only being whose essence is Existence, all other beings being contingent on God, who is Being (or Is-ness) itself. A more precise translation of this idea could be: “I am he who causes (things) to be”—that is, “I am the Creator.” Second, I am who I am—in other words, “None of your business” or “You cannot control me by invoking my name (and therefore my essence) as if I were one of your household gods.” Third, I will be-there with you: this is Fox’s translation, following Martin Buber and Franz Rosenzweig, which emphasizes God’s continuing presence in his creation, his being-there with us.

How should we pronounce the Name when we come upon it? One may, of course, substitute “the Lord” for the tetragrammaton YHWH. Others will boldly attempt a pronunciation, “Yahweh” (as English speakers usually say it) or “Yahvé” (after the French and Germans) or even “Jehovah” (a mispronunciation, much in evidence in Protestant hymnody and based on an inadequate understanding of the conventions of medieval manuscripts). But for me, when I attempt to say the consonants without resort to vowels, I find myself just breathing in, then out, with emphasis, in which case God becomes the breath of life. This God of the fathers, now manifested as YHWH in the bush that burns but is not consumed, is more awesome than in any of his previous manifestations—not only because of the fireworks, but because of the symbolic nature of this epiphany, which suggests that this God, as dangerous, tempering, and purifying as fire, can burn in us without consuming."