"it is our duty to concentrate all our influence to make popular that which is sound and good, and unpopular that which is unsound."

This quote implies that you shouldn't let bad influences be the the only influences around you and make good things seem cool not bad things. you need to make choosing the right a popular and cool thing to do. you need to not let yourself get guided buy the bad things instead be guided by good things, actions, and people.  you need to see farther more then just being 'cool' you need to see and understand how to choose the right 24/7.