The two parts of life, past and future are well merged in this poem. I could see the fire and scorching and burning of the soul from within. It is as if going through a thorough purge before qualifying for another beginning, a "beautiful beginning."
The second part of the poem shows the emerging light, the conquering of the "demons", demons of one's own mind and soul.
I can't guess the reason for the capital "G" in the word "Grin".May be it is bigger than the smirk.
The scene in the inner world is sensitively presented on the physical level with fire and burnt skin imagery.

It flows well.

Write on!