The Gospel of John does not begin with a story, but with a thesis about the whole of reality: "In the beginning was the Logos".
One word, many meanings
Logos is a Greek word of enormous density: it can mean word, discourse, reason, measure, order, intelligence. Philosophers already used it to name the rational order of the cosmos. John takes it up and takes the decisive step: the Logos is not just an abstract principle, it is a person, who "became flesh".
Why the Logos grounds truth
Here is the answer to the question the first step of truth leaves open: why is reality intelligible? Why can our mind adjust itself to things? The Christian answer is that the world can be thought because it was thought before it was made. Reason finds order in Creation because Creation came from a Reason.
This is what Thomas Aquinas called ontological truth: things are true because they correspond to the idea God had of them. The adequation of our mind to the real (logical truth) is only possible because things already are, themselves, adequate to a Mind that thought them. The Logos is the ground beneath the ground.
In-depth study
Church History Course, with Prof. Dr. Rodrigo Bitencourt
In-depth reading of the work of Daniel Rops, where Thomas Aquinas and scholasticism, which ground truth in God, appear in full.
Discover the courseFrequently asked questions
What does Logos mean?
A Greek word gathering the senses of word, reason, order and intelligence. In the Gospel of John, it designates the very Word of God.
What is ontological truth?
The truth of things themselves: they are true because they correspond to the idea God had of them. It grounds logical truth, which is the adequation of the mind to the real.
What does 'In the beginning was the Logos' have to do with science?
Everything: it states that the world is intelligible because it was thought. The confidence that nature has an order the mind can decipher is born of that intuition.
Continue: What is truth · What is alétheia · Truth, goodness and beauty
Source class (NousCast Community): The Idea of Truth (F&T 1.7)