What does the quickening of the spirit mean?

Oh—but the quickening of the spirit!

I cannot tell you what it is like. It is like a symphony compared to one note, like an oratorio compared to the simplest melody, like the poem of Dante, like ineffable Milton, like the crowning light of Shakspeare—all-pervading, all-glorious, like love itself that vanquishes the night of time and pain and death. You are presented to yourself. Your thoughts—all of your past life is impersonated.