What does it mean to “prove that God exists”? Or “prove” that Christianity is true?
As apologists for the Christian faith, people will inevitably ask us to “prove” our claims about God, Jesus, and the Biblical worldview in general. This requires some qualifications and discussion.
If you’ve ever been stumped by the abrupt demand for “proof” of Christian things, it’s because what the unbeliever and us understand as proof. After all, we are the ones who believe the things of God, and it just seems so “self-evidently” true that what the Bible says is valid and real. Most Christians probably don’t think through the issue of proof and evidence external to the Bible, or even that God would need to be proven at all. Here is partly why we find it hard to “prove” our beliefs to others: There is a basic epistemological starting point for knowing the things of God that isn’t evident to those who don’t know Him, as we do.
Think back to your conversion. Was your faith the result of being convinced by rational argument from natural theology about a Designer or a Moral Absolute? Does your faith stand on an inference to the best explanation for existence and morality and purpose? While many of us may have heard these types of arguments and other historical evidences for the Resurrection, etc. what truly converted us was the hearing of the Word. Faith came by hearing and hearing by the Word of God. And conversion was an act on our part, when God granted us repentance and gave us faith to believe in Christ for our salvation. Our knowledge and assurance of all things Christ are supported by the testimony of the Holy Spirit.
Here are some ways the Spirit of God assures us of the truth:
In John 16:14 Jesus says, “He shall glorify me; for he shall receive of mine, and shall show it unto you.
And it is the Spirit that beareth witness, because the Spirit is truth 1 John 5:6
If we receive the testimony of men, the testimony of God is greater; for the testimony of God is this, that He has testified concerning His Son. 10The one who believes in the Son of God has the testimony in himself; the one who does not believe God has made Him a liar, because he has not believed in the testimony that God has given concerning His Son. 11And the testimony is this, that God has given us eternal life, and this life is in His Son.… 1 John 5:9-11
So, from these verses, it is evident that our assurance of the truth is by the Testimonium, the subjective witness of the Spirit to the external Word of God which we believe on.
There is no inference here. There is no abductive reasoning here. There is no probability in these words. It is an immediate knowledge of God from God to our inner man, the spirit, that gives us assurance. Our faith will stand, even though our arguments may fail. Or at least, other will fail to grasp them.
The way to know God then, is not by rational inference, but by immediate knowledge. That is why Romans 1 and 2 establish that the world already has a general knowledge of God, because God has made Himself evident to all his creatures, namely his eternal power and divine nature, which are clearly seen in the cosmos. So why then does the arrogant atheist burden you with the task of proving God if they know God in some way? The answer is staggeringly simple but profound: all people suppress what they know in unrighteousness. They hold the evidence of God in contempt, because of the moral depravity of sin which affects the intellect. The unbeliever literally begins from an epistemology of willing ignorance.
So when asked for proof, explain that God is self-proving, as a matter of common grace. He has put Himself on display by creation and providence. Also remind the interlocutor that not every belief is based on rational inference but some beliefs are self-evident and not provable, yet justified rational beliefs. We cannot prove them, but we cannot deny them without being irrational.
Take the example of proving whether I have a mind or you have a mind that exists. We cannot prove these things, yet it is clear and rationally justified to assume that our minds are real. The same for logic, or experience of the past. The laws of logic are not provable, yet they are absolute and axiomatic when it comes to proving anything else. We cannot not use logic.
God is unique. He is the ontological ground of being for everything else. In reality everything is proof for God, and yet God does not need to be proven as to His existence. God makes Himself known by revelation of Himself to us. Generally through creation, and specially in Scripture.
So to begin in apologetics, begin with this: Don’t attempt to prove God’s existence, for that is not the issue. The issue is that the unbeliever has been suppressing the truth about the God who exists and has disclosed Himself to all sufficiently. Therefore, reason about the God without Whom the unbeliever can prove nothing at all.