There are twelve single Hebrew letters. The twelve reminds us of the twelve zodiacal salts of the twelve zodiacal signs; each one of us belongs to any one of the signs, of both Western and Chinese horoscopes, which are different origins of the same thing.
These twelve single letters symbolize the 12 tribes of Israel. So, we have the twelve tribes of Israel or the twelve salts, twelve archetypes within, and we belong to one of the seven rays, which are the double letters. Why are they called double? Because they go into good and evil, according to our will. Those who do not care about developing spiritually devolve in the negative aspect of that ray. But, that ray is always influencing us, regardless of what we do, because the ray respects the free will of each one of us, this is something we have to understand.