Why does the narrator continue to look forward to his speech even though he is being brutalized?
That is an excellent question. The answer isn't really easy. Why does anyone willingly suffer abuse? There are myriad answers to this question. Perhaps, like many abused/repressed people, Invisible Man is hoping that if he pleases the abuser(s) they will respect him. In the Battle Royal, when all the fighters are eliminated except IM and Tatlock, IM himself says:
"I wanted to deliver my speech more than anything else in the world, because I felt that only these men could judge truly my ability."
This statement suggests that at this point in his life, IM does not respect the values of his own race. He is looking towards white men for validation. He thinks that only they (who are at that very moment abusing him and behaving like beasts) have the ability to judge him--and he desperately wants to meet their standards. At this point in his life, he feels that only white men count. And he knows he must accommodate them if he is to stay in their good graces. Of course all of this occurs before he becomes invisible.
I would add that the speech is his means of expressing his humanity, something universal that racism and the violence of the boxing match cannot take away from him. It's what maintains his dignity, his sense of self-worth--that's why he readily offers Tadlock the prize money.
It's also worth pointing out that throughout the book the narrator looks to his speaking abilities to achieve some measure of contentment in life, but either no one is listening or they are abusing what he has to offer.
The purpose of the narrator coming to this place was to deliver his speech. He shows both strength and weakness, but i would say mostly strength. The battle showed him , that in this day and time and even in the present time, you will have to fight it is a constant battle physically, mentally and emotionally. The others were ready to fight and after they received the "prize" left. The young man knew what his purpose was and that was to show them that black men and people are not for entertainment, we can speak with eloquence. I am glad that he did not let the battle defeat him, that he stood up for what he believed in despite the situation he was put in. Yes black men do look for the approval from the "white man" and they blame them for their short comings, but the battle showed me that the only person you are battling is yourself. don't be invisible , don't blend in with the masses take a stand, stand firm in what your purpose is because in the end you will be rewarded. It was a glimpse or a preview on what the real world will throw at you , insults, hatred, misunderstanding. The battle is never over. The physical battle will make you tougher. you will know how to handle each blow and move pass it.