In the course of reviewing two new biographies of Francis Schaeffer [HT: Between Two Worlds], Douglas Groothuis says the following: [my emphases]
Let me mention two basic ideas that I (as a professional
philosopher, unlike Schaeffer) find profound and helpful.
First, Schaeffer taught that worldviews need to be compared on the basis of
objective criteria. That is, one does not simply presuppose one's worldview
apart from rational testing. Every worldview-or basic perspective on life's
deepest questions-needs to pass three individually necessary and jointly
sufficient tests. First, it must be internally consistent. That is, its
defining beliefs must cohere with one another. Second, a worldview needs to fit
the facts of reality; it must be "true to what is," as Schaeffer put
it. A worldview needs to match the external facts of history and science. (This
shows that Schaeffer held to the correspondence view of truth, not the
"coherency theory of truth," as Hankins claims [91].) Third, a
worldview needs to be livable to be credible. This means that it must pass the
existential test of fitting the facts of the internal world. For example, any
worldview that denies the objective reality of evil (such as secular relativism
or Eastern monism) cannot be lived out consistently, since we intuitively know
that rape, murder, and racism are wrong. These three apologetic criteria can be
nuanced and made much more sophisticated, but they form the backbone of any
solid apologetic method. These truths are far from outdated!
Second, Schaeffer repeatedly emphasized that the God of Christianity was an
"infinite and personal" being, and that humans were not machines or
little gods, but made in the image of this infinite-personal God. In other
words, for Christianity, personality is the deepest and most profound
ontological category of reality-not impersonal time, space, law, chance, matter
or some impersonal sense of deity held by Eastern religions. Schaeffer's
apologetic capitalizes on this uniquely personal sense of reality held by
Christianity. Persons, though fallen, have objective and eternal meaning on
this scheme-as does community, since God himself is a Trinity: a relationship
of divine persons coexisting in one Godhead from eternity.