HELP ASAP Booker T. Washington

In my contact with people I find that, as a rule, it is only the little, narrow people who live for themselves, who never read good books, who do not travel, who never open up their souls in a way to permit them to come into contact with other souls--with the great outside world. No man whose vision is bounded by colour can come into contact with what is highest and best in the world. In meeting men, in many places, I have found that the happiest people are those who do the most for others; the most miserable are those who do the least."

What is the dominant technique used by Booker T. Washington in this passage?​