In his philosophical writings Willard depends on C. S. Lewis' idea of "Real Truth" ("Truth in the Fire: C. S. Lewis in the Pursuit of Truth Today"). But we should start with the fact that within any one form of life (say Base 10 mathematics, geometry, Newtonian Physics, Quantum mechanics, gardening, western medicine, Homeopathic medicine, Ayurvedic medicine, Acupuncture, Reality Therapy) truth is the sum of propositions where we can learn to say "That's true" or "That's False." But there is no such thing as truth across the board, or some metaphysical reality in heaven.
If we want to talk about "God's Eye View of Truth" (Willards's article on "How Concepts Relate the Mind to its Objects") we have to assume that God can say "That's true" to every correct statement in every one of the thousands of activities that humans engage in. He can distinguish every human form of life from every other, and get the language games for each word exactly right in their context. But that is not accessible to us (except by revelation), and there is no point in trying to make an appeal to truth across all forms of life to support an argument.
A similar mistake occurs when we assume and appeal to some metaphysical reality called beauty. Art lovers say "that's beautiful" or "that's ugly" with great confidence, but every different school of art assumes that God is on their side in making such judgments. The French academy said that Van Gogh's paintings were garbage, and he never sold a single picture to the public.
In our day the metaphysical word is justice. "I demand justice." But the word has no meaning except within a form of life in which we can agree that this or that is just or unjust. You can describe justice within Islamic Law, a Marxist State, a Bill of Rights, English Common Law, Napoleonic Law, the latest resolutions of the United Nations, or the many countries where they ask "How much justice can you afford?"
Nor does logic help us to prove or disprove the existence of God. Existence is not a predicate. It is nonsense to say Color exists, Beauty exists, Justice exists, or God exists. The word God is used in hundreds of different ways. In physics it is fashionable to say "Everything points to the Big Bang. Let's call it God." In that form of life it is impossible to be an atheist.
Within the form of life of a masterpiece coming into being (as in Genesis
1), it makes sense to agree or disagree with "This masterpiece came
into being by chance" or "This masterpiece was created by an artist." If
we say "that's true" to "there was a creation" we can go on to give the
Artist a name, Elohim, Yahweh, God, Dieu, Allah, Permeshwar (Hindi), the
Trinity, or whatever." But that is not a logical proof. If the God of the
Bible had allowed us to use logic to prove him, those with a high IQ would
believe in him, and the rest of us would remain ignorant.