"Invictus" is William Ernest Henley's most famous poem. The title, "Invictus," is Latin for "unconquerable. Some say he wrote the poem to affirm his own determination after having his foot amputated as a result of tuberculosis. The poem is famous for its inspirational message and has influenced many historical figures: i. e., Nelson Mandela and Barack Obama.
In the first stanza, the speaker is in a difficult or terrible state. He is ensconced in "night" with its associations of darkness and/or the foreshadowing of death. He describes this state as if it is deep in the depths of Hell: "Black as the pit from pole to pole." Despite being in this hopeless state, he remains resilient and thankful to the gods for giving him an unconquerable soul.
In the second stanza, he adds that despite being in the clutches of poor circumstances, he has not "winced or cried aloud." Despite this bad luck ("under the bludgeonings of chance), he is injured but not is not giving up (his head is "unbowed").
In the third stanza, he adds that beyond his horrible state, death is looming (getting closer). In spite of this and in spite of getting older ("the menace of the years"), he remains unafraid.
His path is difficult and the gate he must pass through is narrow ("strait"). Fate has scripted (the "scroll") punishments for him. These things do not matter because he is the master of his own fate, and more spiritually speaking, he is the captain of his soul. In short, no matter what cruel circumstances he finds himself in, he always returns to faith in himself, in his unconquerable soul; nothing can break his spirit and he will always be positive and will continue to persevere.