I would focus on the inspiration the writings have for us today. There is a lot that can be said, and has been said, about Malcolm X. The truth is that he is a somewhat polarizing figure, but people have been inspired by his ideas and still are.
A variation on what others have said here is that it is never too late to change and become a better person. This might be a good message to high school students since some have them have surely been wasting their potential up to this point in their lives.
Malcolm X made a lot of mistakes. He went to prison for some of them. Other mistakes of his made him famous, but were still mistakes (his strident racial hatred of his early years as a leader). But even with those, even after he'd become famous as a black nationalist, he was still able to change.
So a good point here would be that it's never too late to change, even when people have already gotten a set view of who you are.
In order to make the point that Malcolm X remains a wonderful mentor for the youth of the nation, it might be important to point out that although he seems to embrace violence as a catalyst to racial unity early in his life, he went on to condemn violence later in his life. As a wonderful triumph over adversity and racial prejudice, The Autobiography of Malcolm X also serves as a great example of how writing can truly make a difference in social science! I can't think of a better way to encourage young people to write than by observing the effects of this particular autobiography!
What a wonderful topic for your school assembly! Good luck to you!
This is very broad and will probably be moved to the discussion section. I think that there are a couple of general topics upon which you can speak regarding the work. One overarching theme that really can be understood by adolescents is how Malcolm changes. His identity really undergoes some massive changes in the course of his life and it speaks to how the human identity is a fluid one. This would mean that adolescents do have the power to change themselves over time if they want to do so. Malcolm X experienced some of the worst examples of discrimination and racial injustice. However, he made the conscious choice to rewrite the narrative of his own life. In a world where kids might feel powerless, Malcolm's narrative demonstrates that anyone can have power and can exert it. I think that another talking point would be to simply open up the discussion of how Malcolm X would feel about "the dream" today for people of color, specifically African- Americans. I think that he would have some distinct insights and discussion points about where the nation is on the issue of race relations and where it needs to be. Discussing how Malcolm X saw the dream for people of color during his time and how he would view it today could be another talking point for which you will be able to generate much in way of thought.