It represents God, absolute perfection, the infinite, supreme ultimate. Its color is pure brilliance. Between Kether and Tiphereth lies Daath , the hidden sephira. It represents the bridge over the abyss separating divinity from the not quite divine. The four elements of earth, air, water and fire give a four-point analysis of the universe.
Earth is associated the practical, restraint, sensation etc.
Air is associated with communication, mental-activity, thought etc. Water is associated with emotion, feeling etc. Fire is associated with energy, assertiveness, intuition etc. The eternal mysteries from the face of which the uninitiated cannot lift the veil. He knows that this world and its wisdom are insignificant compared to the greater reality.