Christians impact society in the United States in numerous ways, especially in the field of charity. Some of the Nation's largest charities are or were Christian groups, such as the Salvation Army, the YMCA, individual church groups, etc.
well politically Christians is one of the largest religious groups in America and they also have become political interest groups. Christianity has impacted the ban of gay marriage, the increasing push to overturn Roe vs. Wade, and pro abstinence in schools.
Christianity is one of the bigger religions on the planet. A lot of people are practicing Christians and hold its idealism and moral laws as important in their lives. You have to do some dirty digging on Christianity and see that back in the day, they would go on missions to convert the "heathens" of other nations and worlds. Also, the amount of symbolism "borrowed" from other religions such as Paganism is pretty hefty as well. look at the 10 commandments, they are almost all formal laws in America today. All religions have an impact on society as most religions are the backbone of moral fiber and law in most societies. You need to decide if you are asking for positive impacts or negative impacts on society because impacts in general are just such broad topics.