I began writing a short book to help strengthen the resolve of the men and women in our Church on Apologetics. Last week I posted the Introduction. What follows below is Chapter 1, on the Foundational Necessity of Christianity. See Chapter 2 here.
The fool says in his heart, “There is no God.”Psalm 14:1
Christianity is foundationally necessary to make sense of the actual world we live in. Most non-Christians do not recognize that the very life they are living, the very society they are a part of, the very laws the world operates by, are not possible according to their own worldview. In other words, non-Christians deny God’s existence, yet live in a way that is only consistent with a world in which God exists. What the argument of Foundational Necessity aims to accomplish is to “spiral downwards,” as the famed apologist Cornelius Van Til would say, from the actual phenomenon we experience in daily life to the realities that must be true in order for those phenomena to exist. Taken from a Christian perspective we would say that the real world we inhabit and society we participate in is only possible if the Trinity of the Biblical Scriptures is the foundational reference point for all reality.
Before further explanation of this argument, consider the following illustration. Van Til once travelled on a train bound for Holland. As he looked across his car he noticed a small girl sitting on her father’s lap enjoying the view. At some point during the trip, the girl got upset with her father and slapped him in his face. The irony of the slap, is that it was only made possible because she was sitting on her father’s lap. She was rejecting the very lap she sat on. This precisely illustrates the argument of foundational necessity. Like the little girl on her father’s lap, the simple act of forming a sentence and logically articulating a personal belief that, “God does not exist,” requires the existence of the God of the Bible in order to logically form that statement.
“the unbeliever lives on borrowed capital; that is, he knows the truth deep down and even secretly assumes it, but he has no right to believe it on his own presuppositions–he must borrow from the Christian worldview.”Greg Bahnsen 
Logic Assumes the God of the Bible
Let’s begin with Logic. What is logic? Logic is an invisible force that governs our universe. We all assume the basic principles of logic in order to live every day. Over the years philosophers and great minds have organized simple Laws of Logic to describe the way our universe operates. The Law of Noncontradiction is the simple idea that it is impossible that two contradictory statements can both be simultaneously true. As an example, Jesus either did or did not rise physically from the dead. Both cannot be true simultaneously. The brilliance of this law is in its simplicity. It always works. We depend on this law always working even in the most simple and mundane decisions of life.
Or perhaps The Law of Causality which states that every action has a necessary cause. In other words, within our universe nothing happens spontaneously or without cause. Again, we assume this every day even in the simplest moments of our life. A universe that was not governed by the law of causality would be utterly chaotic and absurd. Any unknown number of events would constantly occur spontaneously and beyond any mechanism for human control. The list of invisible laws that govern our reality is extensive. Even simple arithmetic such as 2 + 2 = 4 is a constant logical reality that both the believer and non believer assume every day will be a consistent reality.
But why do those laws of logic exist? And why are they consistent? Consider the worldview of the Atheistic Materialist who believes that the only thing that exists in the universe is physical matter. They say that nothing immaterial exists. There is no God, there is no spirit, and there is no true self. All that exists is physical matter floating through time and space. The Materialist cannot account for laws like these. After all, what is a law? It is an invisible, universal, non-material truth. When a Materialist states, “There is no God or spirit and all that exists is particles in time and space,” they are assuming that logic exists, otherwise they would not make the statement. But logic in and of itself, is a rejection of their worldview, because logic is non-material. How can the non-material idea of logic actually exist in a universe in which, according to the atheist materialist, nothing non-material can exist?
The only honest way to reckon with the actual world we live in, that is governed by laws of logic is to root those laws of logic in the God who created the universe with order. There is no reason why a godless universe should be ordered. In other words, if the universe ultimately spontaneously erupted into time and space with no cause, we would not expect that universe to have laws of causality, or simple arithmetic. But the simple fact that the universe we inhabit does have laws requires the existence of a lawgiver. Governing principles do not spontaneously create themselves, otherwise we would expect new governing principles to develop spontaneously all the time.
“The only ‘proof’ of the Christian position is that unless its truth is presupposed there is no possibility of ‘proving’ anything at all.”Cornelius Van Til 
Existence & Morality Assumes the God of the Bible
Similarly, consider our existence. At the simplest level, most would admit that we exist. We are real. There is such thing as the self. The only way to explain the self, a human with a mind and emotions and attractions and instincts and memories, is if the God of the Bible created them that way. The non-Christian lives as if the self exists, but when they live that way, they are borrowing from the Christian worldview.
Consider again the Atheistic Materialist who says that all that exists is matter floating through time and space. According to that worldview, there is no true meaning to the self. The self doesn’t really exist in a true way. All we are is space dust that has happened to coalesce into beings that appear to have self-worth and dignity. But according to the Atheist Materialist worldview, self worth, dignity, meaning, and purpose are all just illusions being played out by random particles of space dust floating through time and space. Therefore, when the Materialist argues for morality and argues for human dignity, they are not standing on their own presuppositions, but rather borrowing from the Christian worldview. Their own worldview fundamentally rejects human worth. As atheist philosopher Alan Lightman says,
“I believe that ther is no I, no Self. In my view, and the view of many biologists, the powerful feeling of consciousness and Self is just a name we give to the mental sensation of a hundred billion neurons sending electrical and chemical impulses back and forth in our skulls… I will admit that I’m not feeling cheerful after these ruminations.”Alan Lightman 
It is the Christian worldview that provides a meaningful reference point in God to define our existence. It is the Christian worldview that says that all human beings are created in the image of God and are therefore worthy of life, dignity, and respect. These are assumptions we all live by, but are only consistent with the Christian worldview. It is the Christian worldview that provides foundation for understanding the self as an actual individual, something much more than space dust. Unlike Alan Lightman, the Christian can feel quite cheerful about such a reality.
Meaning & Purpose Assumes the God of the Bible
Let’s consider the importance of meaning and purpose in life. No matter one’s worldview, we all live with some kind of purpose to our lives. Those purposes might be big or small, but purpose is always present behind our actions. For those raising children, one of their driving purposes might be to love their children and care for them well. This is part of their reason for existence, for waking up in the morning. For those aspiring to a better career, their purpose might be to work hard and get promoted. To those who don’t know where their next meal will come from, their purpose is in the pursuit of calories. Many studies have been conducted over the years around the importance of purpose in our lives. One such study was performed at a retirement center, where the retirees were given plants to take care of. The study found that simply having the purpose of keeping a plant alive was enough to extend the life of a retiree by multiple years. Purpose matters, and we all live as though we have one.
Non-Christian worldviews lack a coherent reason for living with a purpose. This does not mean that non-Christians don’t live as if they have a purpose, it simply means that they lack the foundation required to make a purpose meaningful. According to a modern secular worldview that denies God, nothing exists after we die. At the end of history, the sun implodes and every memory, every action ever taken, every good deed, is all eternally forgotten. Nothing lasts. Therefore, any purpose a non-Christian convinces themselves of is ultimately contrived. It passes the time, but amounts to nothing more than a contradiction of their own worldview that demands that no true purpose actually exists.
It is the Christian that lives with a foundation for their purpose. They are Christ-ones, saved and secured for all eternity in the Kingdom of God. Their purpose here on this Earth is to honor God by enjoying Him forever, to live as an, “ambassador for Christ,” sharing the truth of God with all who will here, and expanding the Kingdom of God everywhere they go. Christians pursue justice because actual justice is not only definable through God’s Word, but because we have been given a fixed commission by God Himself to pursue justice. Again, when non-Christians pursue meaning and purpose, they are not living according to their own worldview, but rather borrowing from the Christian worldview.
The One & The Many Assumes the God of the Bible
Lastly, we come to the philosophical quandry of the one and the many. At this point, the reader may be asking ‘Why does the foundation need to be the Christian God? It seems so far that what has been proven is that a God that has communicated his purposes is required for the real world to not descend into absurdity. But how do we know it is the Christian God that is that cornerstone of truth?’ The rest of this book will outline support for the overwhelming clarity to that answer, but foundationally, only the Christian God satisfies the human experience of the one and the many, or as some refer to it, ‘unity and diversity.’
The human experience of life in this universe is such that we daily encounter both differences among all things, and yet an underlying unity that hold all things together. Every snowflake is unique (the many), yet every snowflake is crystalized water (the one). Every human is unique in appearance and personality (the many), yet every human is grown in a womb, and goes through the various phases of adolescence to adulthood (the one). There are a variety of trees (the many), yet every tree fundamentally assumes similar properties that define it as a tree (the one). If you have never engaged in philosophy, it may seem that this is a trivial unimportant phenomenon, but centuries of philosophers have wrestled meaningful with the reason for this phenomenon we experience in this world, and asked whether our universe veers towards monism (the one) or pluralism (the many). The answers philosophers have sought have lead to any number of worldviews with drastically different implications.
It is only the Christian worldview that provides the rich foundation of the Trinity as the answer for why the world is so clearly designed with both unity and diveristy. Before the universe existed, God existed. One God in three persons, Father, Son, and Holy Spirit. All three persons of the Godhead are coeternal with each other, and yet each uniquely distinct from the other. Within God Himself, we have both unity and diversity. His creation is therefore an overflow of Himself. His design reflects His ontological nature.
Consider two opposite errors for considering God. The polytheism the Greek pantheon of Gods believed in a plurality of Gods which lacked unity as a foundational principle. On the other hand, consider Islam. Islam is adamant that God is not a trinity, but is rather one person in one God. With such a God, there is no reason why we would experience the phenomenon of the many. As John Frame has said so well when commenting on a non-trinitarian god such as the god of Islam:
“Such a unitarian god would be unknowable, for we cannot know a blank oneness or an utter uniqueness. The diversity we experience in the real world would not be rooted in any foundational reality.”John Frame 
Only in the Christian triune God is this historic quandry that has plagued philosophers across many times and culture resolved.
Putting It All Together
God is Foundationally Necessary to give an account for the real world we live in. Apart from God, humanity is left wondering if we even exist. Apart from God, there is no reason why a parent ought to love their child, or a mathematician ought to solve a problem, or a doctor ought to heal a patient, or a rational conversation ought to take place. This is not to say that non-believers do not live as if all those things are true. It is imply to say that when the non believer lives as if those ideas are foundationally true, they are borrowing from the Christian worldview, not standing on their own. With no God, none of those elements have actual meaning. When the atheist assumes a logically ordered world, filled with meaning, and virtue, they are not standing on their own worldview, but rather borrowing from the Christian’s worldview. Similarly, the agnostic has no claim to any more coherence than the atheist on any of these issues, because according to the agnostic the founding principle for each of these realities is ultimately unknowable, leaving the agnostic in the same troubling place as the atheist. What’s more, non trinitarian religions outside of Christianity such as Islam or Hinduism also cannot stand up to the full test of foundational necessity because they fail to provide a rational basis to the reality of the one and the many. Only in the tri-une God of the Bible does our existence not deplete into absurdity.
 Pushing the Antithesis. United States: American Vision, 2007. Page 103
 Morley, Brian K.. Mapping Apologetics: Comparing Contemporary Approaches. United Kingdom: InterVarsity Press, 2015. Page 80.
 Lightman, Alan. Searching for Stars on an Island in Maine. United States: Knopf Doubleday Publishing Group, 2019.
 Frame, John M. Apologetics to the Glory of God: An Introduction. United States: P&R Pub., 1994. Page 50.