Out of the night that covers me,
Black as the pit from pole to pole,
I thank whatever gods may be
For my unconquerable soul.
In the fell clutch of circumstance
I have not winced nor cried aloud.
Under the bludgeonings of chance
My head is bloody, but unbowed.
Beyond this place of wrath and tears
Looms but the Horror of the shade,
And yet the menace of the years
Finds and shall find me unafraid.
It matters not how strait the gate,
How charged with punishments the scroll,
I am the master of my fate:
I am the captain of my soul.
Darkness is a metaphor for evil, and perhaps depression, "The Pit" is Hell. The writer, in thanking the Gods for his "unconquerable soul" is meaning that whatever bodily adversity he faces, his soul will remain unconquered.
The second verse repeats the theme, the body may be broken, but not the spirit (Fell = bad or evil)
The third verse talks about the "Place of wrath and tears" meaning the physical worls (Cf the Burial Service from the book of common prayer, refering to life as "this vale of tears" (Wrath = anger) and also the "Horror of the Shade" which is a poetic expression for Death (Shade = a ghost or spirit) and even faced with both of these the writer is unafraid.
"Strait the gate" is a biblical reference (Strait = narrow) the last two lines repeat the main theme, that a person is responsible for their self, whatever happens in