More from Machen to end the week:
The Church of today has been unfaithful to her Lord by admitting great companies of non-Christian persons, not only into her membership, but into her teaching agencies. It is inevitable that some persons who are not truly Christian shall find their way into the visible church; fallible men cannot discern the heart, and many a profession of faith which seems to be genuine may really be false.
But it is not this kind of error to which we now refer. What is now meant is not the admission of individuals whose confessions of faith may not be sincere, but the admission of great companies of persons who have never made any really adequate confession of faith at all and whose entire attitude toward the gospel is the very reverse of the Christian attitude.
Such persons, moreover, have been admitted not merely to the membership, but to the ministry of the Church, and to an increasing extent have been allowed to dominate its councils and determine its teaching.
The greatest menace to the Christian Church today comes not from the enemies outside, but from the enemies within; it comes from the presence within the Church of a type of faith and practice that is anti-Christian to the core.
Gresham Machen, Christianity & Liberalism, p. 159-60