Paul warned the elders of the church in Ephesus about the critical need for them to be vigilant: “Pay careful attention to yourselves and to all the flock, in which the Holy Spirit has made you overseers, to care for the church of God, which he obtained with his own blood. I know that after my departure fierce wolves will come in among you, not sparing the flock; and from among your own selves will arise men speaking twisted things, to draw away the disciples after them. Therefore be alert…” (Acts 20:28–31). This apostolic warning was not just for the Ephesian church; it is a warning that is necessary for every church in every age.

Paul’s warning was taken very seriously by many churches and ministers in the controversy between fundamentalists and liberals in the 1920s. Fundamentalists seeing their churches and schools deserting historic Christianity viewed liberals as devious, deceptive, even demonic. Dr. J. Gresham Machen, in the most valuable and enduring critique of liberalism written in the 1920s, Christianity and Liberalism, concluded that Christianity was one religion and liberalism was quite another.

While Dr. Machen was often seen as the greatest intellectual leader of the fundamentalist movement, he was not entirely comfortable with the fundamentalist movement. He did not believe that it was enough to defend just five fundamentals of the faith. For Machen, true Christianity was an historic community with a full and coherent theology. True Christianity, as Dr. Machen knew it in the Reformed tradition, came to doctrinal expression in a full confession of faith, such as the Westminster Confession of Faith.

Dr. Machen believed a confession expressed the mind of the church and showed church members what the church confessed as the great and necessary teachings of the Bible. The confession should serve as an antidote to doctrinal ignorance in the church as the church diligently teaches its confession to its members. The confession should show the church what doctrines it must fight to uphold. It should strengthen the church as the bulwark of the truth.

Today, evangelical churches face doctrinal challenges every bit as serious as those of the 1920s. Some evangelicals reject the inerrancy of the Bible. Some reject the historic doctrine of God for what they call “open theism.” Some reject the biblical doctrine of justification that was recovered by the Reformation for some form of moralism.

Paul’s call to thoughtful vigilance is needed more today than ever. Ministers, elders, and church members today must be renewed in the truth by a full and careful knowledge of doctrine contained for us in the great confessions of the churches. Then we will know where and when to fight, as well as the truth for which we fight. As Paul wrote to Timothy: “Keep a close watch on yourself and on the teaching. Persist in this, for by so doing you will save both yourself and your hearers” (1 Tim. 4:16).