Sentence:  And he pointed with his little assegai, the assegai handled with the royal wood, to where the fire glowed reddest—ay, he pointed and laughed. Then, my father, I grew cold indeed—yes, I grew cold who soon should be hot, for I saw the purpose of Chaka. He would put me to the <WSD>trial by fire</WSD>. 
Meaning of the word marked with <WSD> tags:  A test in which a person is exposed to flames in order to assess his/her truthfulness, commitment, courage, etc.