The four letters Y, H, W, H stand for the Hebrew letters Yod, Hey, Waw, Hey. The Holy Name YHWH represents the Divine in both His Masculine and Feminine Aspects: the Yod and the first Hey respectively represent He and She, Who manifest Themselves; and the Waw and the second Hey respectively represent He and She, the Thinker.
There has always been a special care so that the Holy Name is not invoked in an improper or casual way, in keeping with the 3rd Commandment (“You shall not take the Name of YHWH your God in vain”). Due to a decline in spiritual consciousness, the sages of Israel over time increasingly restricted Its utterance, until it was finally totally discontinued (following the destruction of the second Temple of Jerusalem, in the year 70). It is now replaced, in traditional jewish prayer, by the Holy Name “Adonay”, which means “Lord”, and in speech by the expression “Hashem”, which means “The Name”.
Since, the pronunciation of the Holy Name came to be forgotten.
With the Revelation of the Eternal Book, it is once again revealed. However, care is still taken so that the Holy Name is not invoked in an improper way, or casually. For that reason in particular, and, globally, due to the sacredness of Its Dimension, It is not fully transliterated.
The first Hey is pronounced like a deep “A” sound, as in “Jar”, and the second Hey is pronounced like a lighter “A”, as in “Advent”.
The Holy Name is also manifest in short form, composed of the first two letters Yod and Hey. Its pronunciation, which has been retained traditionally, is: “YA”, as in the evocation “Halelu YA”, “Praise YA”, “Praise the Father and Mother”.