“If you can dream—and not make dreams your master;”

What does he mean by this?

The line, “If you can dream – and not make dreams your master” is a very important principle for having balance. Meaning, dreams should not be your only aspirations, goals, or thoughts. ... This quote means that people should not be a slave to their dreams, constantly working for their dreams and wishes.

I have answered this before

"character is what you are in the dark." dwight lyman moody, in this very witty quotation of his, states we act and think differently when we are "in the dark", that is, when the spotlight is not on us and everyone can see us and consequently judge us. when reading, we tend to be sympathetic to some characters and their dilemmas. by being so, we are saying to ourselves that we agree with those characters' acts and choices, even if they are morally questionable if we have common sense in mind. dwight lyman moody's quotation applies very well to "crime and punishment", by   19th century russian writer fiodor dostoyevsky. raskolnikov, the main character, a former law student who spends his days reflecting upon life and its misery, draws a fatal conclusion: mankind is divided in two main categories: ordinary and extraordinary people. the first are the ones who lead a run-of-the-mill existence and are full of imperfections; the latter are the ones who are spiritually superior, the ones who always know better, and have the right to judge the ordinary ones, as well as eliminate them if for common good. raskolnikov considers himself as belonging to the extraordinary category and decides to kill an old lady who is a money lender and in whose house he rents a small room. raskolnikov compares himself to napoleon, who had the undeniable right to execute tons of people during the war in order to save his nation. of course what the main character decides to do is a horrendous crime, but as readers we feel it is the right thing for him to do, since the victim is a mean old woman who only thinks about money and keeps humiliating her younger sister. what one experiences is a mixture of sympathy and empathy for the character, even though he decides to commit homicide, which is not at all accepted or tolerated by civilized citizens. however, since readers are "in the dark", they allow themselves to feel in ways they would probably never dare to confess to anyone, no matter how nasty or vicious a character can be. after all, they are just reading and doing no harm. in other words, readers are in the dark and can be who they are without being judged.