This is an interesting question. I think that the writer is likely addressing readers who are sitting on the fence, hesitant about going after their dreams. Or, perhaps, the person who feels strongly about an issue but is afraid to act on his or her feelings because those feelings go against the norm. The poem speaks to those individuals who have a dream (which is all of us, really) who might be afraid to go after that dream because something is holding them back.
Look at it line by line.
The first line tells us to cast away rules. We live by so many rules in our society - from the rules that are parents make (many of which should NOT be broken because they are for our own safety) to the rules that society and peer pressure force upon us such as we must get married, have children, work a steady job in a traditional field, or even accept things just because we are told to accept them. Think abut it this way - if people like Martin Luther King, Jr. and Rosa Parks had not broken society's rules, where would the Civil Rights movement be?
The second line tells us to follow our hearts. Sometimes, our heart knows right from wrong better than society does. Many people opposed slavery well before the emancipation proclamation was written. Society said it was acceptable, but they knew in their hearts that enslaving another human being was wrong. Thise who spoke out even though they knew they might be ostracized for it followed their hearts. Many a performer, athlete, or even entrepreneur was once told that he or she was going after something that would never amount to anything, but those who reach the top got there because they followed their hearts.
The last line ties to the second nicely. When we look into our soul, we become even more aware of what is right in general and what os right for us as individuals. Only we know what is true deep inside of ourselves.