The Letters And Their Substance

Question: Why are the spiritual levels that descend downward changed while the letters on them remain the same?

Answer: Letters are directives from the Light so they are unchanged. Only the material from which they are composed is changed. The letters themselves, being similar to the Light, are not subject to change, whereas their substance, still, vegetative, animate, or Human, meaning the desire constantly changes.
[196745]
From the Kabbalah Lesson in Russian 7/17/16