Harnack states in the Preface that he is making an attempt to "determine exactly" the second source of St Matthew and St Luke (Q), and is moved to do so by Wellhausen's "Introduction to the First Three Gospels" (1905). He counts the words "which occur in these gospels and do not occur elsewhere in the New Testament". Suggests that "it is thus possible to construct the fairly extensive text of Q". Preface v.

The author hopes that his publication will end the "wild hypotheses" regarding the history of the Lord. Perhaps mistaken. He goes on to concede: "The temptation to confine one's gaze to isolated details, and to view these as reflected in the distorting mirror of prepossession and prejudice, without deep and reverent study of tradition, is too great for us to expect that these strivings will ever cease."