“Jehovah” means “I am” and “to be,” as is generally known. We know from the Book of Creation, or Genesis, that God was called “Jehovah” from most ancient times. In the first chapter he is called “God,” but in the second and subsequent chapters he is called “Jehovah God.” Later on the descendants of Abraham through Jacob forgot the name of God owing to their long sojourn in Egypt. Then in the event recorded in the following passage it was recalled to memory:
Moses said to God, “What is your name?” God said, “I Am I Who Am. So you will say to the Children of Israel, ‘I Am sent me to you.’ And you will say, ‘Jehovah, the God of your fathers, sent me to you.’ This is my name to eternity, and this is how I will be remembered from generation to regeneration.” (Exodus 3:13–15)
Since God alone is “I Am” and being, or “Jehovah,” therefore nothing exists in the created universe that does not derive its underlying reality from him. (How this happens will be discussed below [Sections 21, 75, 76, 78].)
The same thing is meant by these words: “I am the First and the Last, the Beginning and the End, the Alpha and the Omega” (Isaiah 44:6 and Revelation 1:8, 11; 22:13). This means that on every level of existence he is the one and only entity, the source of all things.
God is called the Alpha and the Omega, the Beginning and the End, because alpha is the first letter in the Greek alphabet and omega is the last; so together they mean all things as a whole.
In the spiritual world, every alphabetical letter has a meaning. A vowel, because it carries tone, means a feeling or some kind of love. Spiritual and angelic speech, and also writing, depends on these meanings—but this is a mystery that has not been known until now. There is in fact a universal language shared by all angels and spirits. It has nothing in common with any human language in our world.
After death everyone inherits that language, because it is latent in everyone from creation. In the spiritual world, then, everyone can understand everyone else. I have often been allowed to hear that language. I have compared it with languages in the physical world and have ascertained that it has not even the least thing in common with any earthly language. It differs by its very origin, which is that every letter of every word has a meaning. This is why God is here called the Alpha and the Omega, meaning that on every level of existence he is the one and only entity, the source of all things.
from True Christianity, Volume 1, Section 19