It's difficult to underestimate the impact of Christians to "our society," by which I assume you mean primarily US society. It's worth noting, however, that Christianity is responsible for the modern global calendar, with the year 0 set as the year of Jesus Christ's birth.
The first permanent European settlers in the United States, the pilgrims, were Christian. The strict Puritan (Christian) tone they set still reverberates in parts of the US. Due to the Christian precept of resting on Sundays, most businesses were closed on that day until about 50 years ago—and many businesses still are (notably the fast-food restaurant Chick-Fil-A). Our Christian heritage has resulted in the words "In God We Trust" appearing on US money, and the words "one nation, under God" in our Pledge of Allegiance. Witnesses in US courts used to swear to tell the truth "so help you God," while placing their hand on a Christian Bible. Nearly every United States president has been an avowed Christian, ritually attending church on Sundays. And almost every American native, Christian or not, is familiar with famous stories and characters from the Bible. It's steeped into US culture.
Christians have also played a divisive role in the US, as well as worldwide. A series of scandals involving high-profile Christian preachers over the past four decades has weakened people's perceptions of the faith. Recent revelations of rampant pedophilia in the Catholic Archdiocese are horrifying. Other religions, particularly Islam, are on the rise, and some of their tenants conflict with those of Christianity. This has resulted in polarization, with Christians, unfairly or not, often branded as intolerant, out-of-touch conservatives. One particular Supreme Court decision Roe v. Wade exemplifies the split between the Christian viewpoint (abortions should be outlawed) and the secular view and current law (abortions should be legalized).
Though polls show that fewer people profess to be Christian (or sometimes any religion), Christianity is still the largest religion in the United States, and the world. It has impacts on the United States, as well as other countries, both obvious and subtle. For example: Christmas. While we might have eventually created some sort of December holiday, it was the fourth-century decision to celebrate Christ's birth on Dec. 25th that set the tone for our current Christmas day and the ensuing winter holiday season.