The letter Shin ש relates to the trinity, the three primary forces. It is the creative fire at the base of life. It is the fire that enflamed the burning bush before Moses. ש Shin represents the power of creation inherent in every atom, a power that we must harness and direct towards liberation, rather than using our energies to degenerate ourselves further.
Shin
In Kabbalah, the letter ש Shin is the symbol of fire. The divine fire has three wicks as the letter ש Shin has three wicks, which represent the trinity. That trinity is Kether, Chokmah, Binah, Father, Son and Holy Spirit, the First Logos, the Second Logos and the Third Logos.
In Kabbalah, in the Zohar, it is stated that the letter Shin also represents Chesed, Geburah, and Tiphereth [the Monad]. We will say that inside of us we have the letter Shin.
Single Letters
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.