Here’s J. Gresham Machen’s answer from the conclusion to his provocative 1933 essay “The Responsibility of the Church in Our New Age”:
“The responsibility of the church in the new age is the same as its responsibility in every age. It is to testify that this world is lost in sin; that the span of human life–no, all the length of human history–is an infinitesimal island in the awful depths of eternity; that there is a mysterious, holy, living God, Creator of all, Upholder of all, infinitely beyond all; that he has revealed himself to us in his Word and offered us communion with himself through Jesus Christ the Lord; that there is no other salvation, for individuals or for nations, save this, but that this salvation is full and free, and that whoever possesses it has for himself and for all others to whom he may be the instrument of bringing it a treasure compared with which all the kingdoms of the earth–no, all the wonders of the starry heavens–are as the dust of the street.
“An unpopular message it is–an impractical message, we are told. But it is the message of the Christian church. Neglect it, and you will have destruction; heed it, and you will have life” (in Selected Shorter Writings, edited by D.G. Hart, 376).