Answer
Bible-thumper is a mildly derogatory term for someone who is deemed overly zealous in his or her Christian faith, especially if the zeal is attended by a “preachy” attitude. The dictionary.com definition of Bible-thumper is “an evangelist or other person who quotes the Bible frequently, especially as a means of exhortation or rebuke.”
The first use of the term Bible-thumper traces back to the early 1920s. The timing makes sense. Fundamentalism was on the rise, having been formalized in the late nineteenth and early twentieth centuries. The Fundamentalists were conservative Christians who were concerned that the moral values of society were being eroded by modernism and a disregard for Scripture. The Fundamentalists refuted liberal, “higher criticism” theologians who denied the literalness and reliability of the Bible. When liberal Christians embraced Darwinism as the best explanation for all life on earth, Fundamentalist preachers, teachers, and scholars united in calling the church to hold firm to the “fundamentals of the Christian faith.” The response of the secular world was dismissive: such backward preachers were nothing but wild-eyed, pulpit-pounding “Bible-thumpers.”
One can imagine a Fundamentalist preacher giving a sermon, pointing to this or that passage and “thumping” his hand on the Bible while declaring, “This is God’s Word!” That would be a literal Bible-thumper. Today, someone may be called a Bible-thumper if he is serious about following the Bible’s teachings, if he speaks out against moral rot, or even if he evangelizes. The term is loosely and subjectively applied and used mostly as an insult.
The insult may be deserved for some believers who act as if they know how everyone else should live and constantly cite Bible verses to justify being a know-it-all or busybody. On the other hand, Bible-thumper is an unfair label for a Christian sincerely doing his best to live according to God’s Word.
If a well-intentioned, loving Christian is called a Bible-thumper by prejudiced or mean people, he or she should probably take it as a compliment. After all, bringing attention to the Bible is not a bad thing. And Jesus Himself was called “demon-possessed” (John 7:20), a “Samaritan” (John 8:48), a “glutton and a drunkard” (Matthew 11:19), and a blasphemer (Mark 14:64). Paul was called a troublemaker and insurrectionist (Acts 16:20–21; 19:26). The term Christian likely began as an insult (Acts 11:26). Someone in the first century coined the term to tag the crazy fanatics who were turning “the world upside down” (Acts 17:6, ESV). What? You actually believe an executed Jewish rabbi rose from the dead? Are you a Christian or something? The early believers were encouraged to wear the insult proudly; they embraced the term Christian, wearing it as a badge of honor: “But if you suffer as a Christian, do not be ashamed, but praise God that you bear that name” (1 Peter 4:16).