"Mere Christianity" was the term C. S. Lewis employed to describe essential Christianity--those core Christian beliefs held through the ages by Catholics and Protestants alike. What most people don't realize is that Lewis adapted this term from an author who wrote more than three hundred years ago. The author's name was Richard Baxter, and his writings on the "essentials" of Christianity provide a useful background to the views articulated by Lewis.
A Protestant clergyman in England, Baxter lived from 1615 to 1691. Though all but forgotten today, Baxter was a popular and prolific author in his own day and for many decades following his death. He wrote more than 160 separate works--nearly 200, by some estimates. One Anglican Bishop said of Baxter that had he lived during the earliest years of Christianity, he would have been "one of the fathers of the church." The famed Dr. Samuel Johnson, when asked by Boswell which books by Baxter he should read, replied: "Read any of them; they are all good." In particular, Dr. Johnson thought that Baxter's Reasons for the Christian Religion "contained the best collection of the evidences of the divinity of the Christian system." Many years after Baxter's death, famed English statesman William Wilberforce called Baxter's writings on the spiritual life "a treasury of Christian wisdom."
I am a CHRISTIAN, a MEER CHRISTIAN, of no other Religion; and the Church that I am of is the Christian Church, and hath been visible where ever the Christian Religion and Church hath been visible: But must you know what Sect or Party I am of? I am against all Sects and dividing Parties: But if any will call Meer Christians by the name of a Party, because they take up with Meer Christianity, Creed, and Scripture, and will not be of any dividing or contentious Sect, I am of that Party which is so against Parties: If the Name CHRISTIAN be not enough, call me a CATHOLICK CHRISTIAN; not as that word signifieth an hereticating majority of Bishops, but as it signifieth one that hath no Religion, but that which by Christ and the Apostles was left to the Catholick Church, or the Body of Jesus Christ on Earth.