How we cite our quotes: (Line)
Quote #1
Take up the White Man's burden-- (1, 9, 17, 25, 33, 41, 49)
The way this refrain is put together (this "burden" belongs to the "White Man" alone) emphasizes the fact that this job of "civilizing" the world can only be one by one group of people. It's almost like a Mission: Impossible scenario, saying "Your mission, if you choose to accept it…" The poem tries to emphasize the notion that white men have a duty to do this work.
Quote #2
To wait in heavy harness, (5)
The duty won't be comfortable either. Even still, this metaphorical comparison with a team of horses pulling a wagon communicates the speaker's belief in the strength of white men to get the job done.
Quote #3
In patience to abide,
To veil the threat of terror
And check the show of pride; (10-12)
When the speaker gets more specific about this burden, we realize that the duty is framed in pretty selfless ways. The white men will be easing fear and acting humble. That sounds like work we can get behind (until, you know, we realize that it's for white men only).