There is one dominant theme in this quotation. It is the idea of courage. It is always easier to go with the the majority view. But when you have to stand for what you believe in and it goes against the majority, it can be a daunting task.
There are two other points in this quote that add to this idea of courage. The word "defend" also points in this direction, because there is a sense that others are "attacking" your views. This is why you will have to defend what you believe.
The other word is "world." This implies that the majority of the people in your community hold a different point of view. It is as if to say that you will have to go against the world. From a sociological point of view this is incredibly hard. Foucault's quote on how power works can give you some great insights:
"Each society has its régime of truth, its ‘general politics’ of truth: that is, the types of discourses which it accepts and makes function as truth; the mechanisms and instances which enable one to distinguish true and false statements, the means by which each is sanctioned; the techniques and procedures accorded value in the acquisition of truth; the status of those who are charged with saying what counts as true."
In short, courage is the theme.