“Let us ask those who possess nothing but church membership, and yet want to be called Christians, how they can glory in the sacred name of Christ? For no one has any communion with Christ, but he who has received the true knowledge of him from the word of the gospel. The apostle denies that anyone actually knows Christ who has not learned to put off the old man, corrupt with deceitful lusts, and to put on Christ. External knowledge of Christ is found to be only a false and dangerous make-believe, however eloquently and freely lip servants may talk about the gospel. The gospel is not a doctrine of the tongue, but of life…It is fully understood when it possesses the whole soul, and penetrates to the inner recesses of the heart. Let nominal Christians cease from insulting God by boasting themselves to be what they are not, and let them show themselves disciples not unworthy of Christ, their master.”
John Calvin, Golden Booklet of the Christian Life (quoted by Paul R. Schaefer Jr. in The Spiritual Brotherhood, 58).