This is because the Sefirot are Godliness. Change from state to state is simply not applicable to Godliness. If so, the light of the Sefirot is not something new. The inference is that the light of the Sefirot was there from before. If the visibility of this light were part of its intrinsic nature, it would always have been visible. In that case, what was new? What was new was that God willed and made it possible for the light of the Sefirot to be seen. He gave this permission at precisely the moment He wished, not before. The change was not in the nature of Godliness. The change was in its being revealed to recipients.