Logos, the principle of the self-manifestation of God. God manifest to himself, in himself: that is His Logos. Therefore whenever God appears, to himself and to others outside of himself, it is the Logos, the self-manifestation of God, which appears. This Logos is also, and in a unique way, in Jesus as the Christ. And this, according to the Apologists, is the greatness of Christianity. This is the basis for its claim for salvation, because if the Divine Logos in its fulness had not appeared in Jesus as the Christ, then no full salvation would be possible. This is the argument ex existentia, from existence, and not from speculation. Please remember what I said before, that all these seemingly speculative ideas into which we must now dive, are only seemingly speculative. Of course, speculative means “looking at” problems, and in this sense they are speculative. But they are not produced for the sake of speculation, but for the sake of making Christian salvation understandable. And in all decisive moments of the struggle between the different movements, we find that the classical theologians, who finally win the victory, refer to salvation and then say: If there shall be salvation: there must be this concept of the Logos. That is always their arguing. There is salvation; we have experienced it – so we must speak in this and that way about the Logos.

Paul Tillich, A History Of Christian Thought – Table of Contents