In his opening lecture, Harnack lays out his basic hermeneutical method as he strives to explain the essence of Christianity. That method may best be described as making a distinction between the kernel and the husk, that is, between that which is essential in the message of Jesus and that which is incidental and bound by the historical circumstances in which Jesus lived. Let us hear Harnack in his own words:
Jesus Christ and his disciples were situated in their day just as we are situated in ours; that is to say, their feelings, their thoughts, their judgments and their efforts were bounded by the horizon and the framework in which their own nation was set and by its condition at the time. Had it been otherwise, they would not have been men of flesh and blood, but spectral beings ... To be a man means, in the first place, to possess a certain mental and spiritual disposition, determined in such and such a way, and thereby limited and circumscribed; and, in the second place, it means to be situated, with this disposition, in an historical environment which in its turn is also limited and circumscribed ... From these circumstances it follows that the historian, whose business and hightest duty it is to determine what is of permanent value, is of necessity required not to cleave to words but to find out what is essential. (pp. 12-13)
Harnack explicitly approaches the question, "What is Christianity?" more as a historian than a theologian. Indeed, Harnack's historical investigations on the apostolic fathers, his 3-volume study of the history of Christian dogmatics, and his work on The Mission and Expansion of Christianity in the First Three Centuries, are all helpful historical studies and retain their value even today. Perhaps the church historian should have remained in his own bailiwick and not ventured into the realm of theology. But venture he did, and what we need to recognize is that he ventured into that realm using the methods, tools, and habits of thought of the historian, and the particular kind of historian who, in good German fashion, thinks of history as the evolution and unfolding of grand ideas.
To return to Harnack:
[Thinking historically] helps us to grasp what is essential in the phenomena, and to distinguish kernel and husk ... [The Gospel] contains something which, under differing historical forms, is of permanent validity. (pp. 12, 14)
In particular, Harnack argues that though Jesus came within the historical context of the Judaism of his day, Jesus' teaching has only a loose connection with Judaism. Thus, for Harnack, it is not absolutely important to become intimately acquainted with the various sects of Judaism, or with their apocalyptic fervor and messianic hopes.
The oftener I re-read and consider the Gospels, the more do I find that the contemporary discords, in the midst of which the Gospel stood, and out of which it arose, sink into the background. I entertain no doubt that the founder had his eye upon man in whatever external situation he might be found--upon man who, fundamentally, always remains the same. (p. 17)
For Harnack, then, the aspects of Jesus' (or John the Baptist's) teaching that focus on a coming day of judgment, about an axe being laid to the root of the trees, about unquenchable fire, or sitting on twelve thrones judging the twelve tribes of Israel--all of this is mere "apparatus" (p. 41), mere husk that is not essential to the core message of Jesus concerning the soul's individual relationship with God.
What, then, is the core message?
The Christian religion is something simple and sublime; it means one thing and one thing only: Eternal life in the midst of time, by the strength and under the eyes of God. (p. 8) ... It is not a question of angels and devils, thrones and principalities, but of God and the soul, the soul and its God. (p. 56, cp. p. 142)
I'll have more to say about this core message in future posts, but it is enough to meditate on that thought, "God and the soul, the soul and its God."