One of the best examples of Christian's impacting the society they were living in was the publication of Uncle Tom's Cabin by Harriet Beecher Stowe. As the society at large attempted to insulate itself from the truth that the American form of slavery was abhorrent to God, she creatively and persuasively used the media form of her day to effectively communicate the truth about what slavery was really all about. She addressed the pertinent issues directly, and even showed the hypocrisy of many northern abolitionists. In the end, the mask that society had used to protect itself from being confronted with the truth was removed, and slavery was abolished.
A more recent example is the modern creationist movement. When The Genesis Flood was published in 1961, almost no one in the scientific community, and very few people in the society at large felt that strict creationism could ever be defended successfully when challenged by the leading scientists of the day. When most, if not all, the secular journals refused to even look at articles written by creationists, Henry Morris and Duane Gish went on the offensive by challenging leading scientists on university campuses to creation/evolution debates. They entered the arena of academia with truth, and successfully "attacked the city of the mighty." As a result of their efforts, thousands of scientists have been convinced of the truth of their position, and the general public is becoming increasingly interested in discussing the issue of Evolution vs. Intelligent Design.