This has already been explained in the Zohar on the subject of the alphabet. This idea is not just an analogy but a depiction of the reality that all the visible letters of The Torah are a representation of 22 supernal lights and these lights illuminate the letters lending sanctity to a Torah scroll, Tefillin, Mezuzot and Kitvei Kodesh. Accordingly, the more sanctity invested into those writings, the greater the influence and shine are imparted via the letters. Therefore, a Sefer Torah with one mistake invalidates the whole preventing the ability to influence and draw holiness to the congregation during its reading.