For unbelievers, there are only a few ways to prove that God exists, depending on how willing they are to accept God's existence. For unbelievers who are willing to believe in God, they often only need to be told about God and Jesus Christ in order to believe. This group makes up a large portion of unbelievers, and it is why missionaries are often so successful.
God will then prove his own existence to these unbelievers, because they are willing to receive his evidence of answered prayers.
According to Paul, no one has an excuse to not believe, because God's creation is evidence enough. Paul says, "For the invisible things of him since the creation of the world are clearly seen, being perceived through the things that are made, even his everlasting power and divinity; that they may be without excuse." (Romans 1:20 WEB)
Truly the creation of the world, and the fact that the entire
universe exists within extremely narrow boundaries of physics, is plenty
of evidence even for
highly knowledgeable individuals (i.e. scientists). This is why there are some scientists who believe in Intelligent Design.
However, on the other end of the unbelief spectrum, there are some unbelievers who will refuse to believe unless they see an impossible miracle happen before their eyes. There are even some people who would still refuse to believe, even if they witnessed a miracle. They would be convinced it was a trick.
When Paul witnessed to the Corinthians, he says that those who believed had become Christians because of the power and miracles of the Holy Spirit, rather than his words. "My speech and my preaching were not in persuasive words of human wisdom, but in demonstration of the Spirit and of power, that your faith wouldn't stand in the wisdom of men, but in the power of God." (1 Corinthians 2:4-5 WEB)
However, there were likely people who saw these miracles and
still did not believe. For these unbelievers, they will not believe no matter what they see, and there is nothing we can do to convince them.
God will have to convince them, although in reality all conversions are the work of God's Spirit anyway. Paul explains, "I planted. Apollos watered. But God gave the increase. So then neither he who plants is anything, nor he who waters, but God who gives the increase." (1 Corinthians 3:6-7 WEB)
Everyone will be convinced eventually, when they are face-to-face with God on judgment day, but it will be too late for salvation then.
Unlike these extreme doubters, there is a group of unbelievers who are in between these two extremes described above. These unbelievers can be convinced with a logical progression of thoughts that answer questions they have about God's existence.
The following is one example of how to prove that God exists to one of these unbelievers who can be convinced with logic.
If a God does exist, might he communicate with people?
Yes, if a God does exist, then it is reasonable that he may want to communicate with people. Pretend you are God and you created people. Would you want to talk to them? Maybe you do not feel the same about people as God does, so instead of people, imagine that you created a bunch of kittens or puppies. How do you feel about them? If you have the capacity to communicate with them, would you? What might your message to them be? Would you want them to hurt each other?
If a God does exist, and he wanted to communicate to people, then how might he communicate?
If a God does exist, what options does he have? Would he communicate with people by talking directly to them? What other options are there for him to talk to someone?
Not only is it reasonable that God would talk to people, but it is also reasonable that he would communicate in a way that makes sense to the individual. Otherwise, God's communications would be pointless if he speaks in a foreign language or in concepts the individual does not understand.
Now consider, if God appeared before you in bodily form and spoke to you, would you tell others? Or consider it like this: If a giant angel appeared before you and spoke to you, would you tell others?
You might think that you would be hesitant to tell others, because maybe no one would believe you. However, when something unbelievable happens to us, the typical human response is to tell everyone. "You wouldn't believe what just happened!" or "You're not going to believe this, but..."
If you met with the Creator of the universe, it is reasonable that a person would want to tell everyone, just as you would tell people if you met someone famous. Likewise, if you felt this interaction was extremely important, then it is also reasonable that you would want future generations to know about it.
However, how would you tell someone in the future of your experience? There are not very many options for communicating to future generations. We know throughout history that people wrote things down, and even now people continue to write things down to preserve their thoughts and experiences.
If an immortal God does exist, is it reasonable that he would be consistent over the course of thousands of years?
Let's imagine that God wanted to tell people something, so he tells one person and instructs them to tell everyone else. However, no one believes the person and they ignore the message. Then, several hundred years later, God tries again. A few people believe the person, but most people do not believe. This process repeats itself, and eventually there are a collection of writings regarding each person's experience with this God.
If God does exist and is immortal, is this flow of events reasonable?
Yes, if God has tried to communicate with people, then it is reasonable that people might write their experiences down. Furthermore, it is reasonable that eventually there might be a collection of these interactions spread out throughout hundreds or even thousands of years. Additionally, it is reasonable that the "God-character" in these writings would be consistent.
However, what if not all the writings agree? These individuals are all witnesses to a self-proclaimed experience with God, so who do you believe when the witnesses disagree about God?
Who do you believe when witnesses disagree?
Imagine that you are a police officer and you arrive at a car accident. There are five people who saw the car accident happen. All of these people are complete strangers to each other: no one has ever met anyone else before. Four of these people have the exact same story about how the car accident happened. However, the fifth person disagrees completely with the other four.
Who do you believe? Let's say that the evidence from the car accident could support either story. Do you believe the four people who have similar stories about what happened? Or do you believe the one person who disagrees completely?
While it is actually very unreasonable to believe the fifth person, what if you find out that the fifth person actually showed up several minutes after the accident happened? Meaning, the fifth person did not actually see the accident. Or what if the fifth person saw the accident from really far away, while the other four were right there when the accident happened?
Would you believe the fifth person? Or would you believe the other four people, who all agree on a very similar order of event?
Now, let's consider the Bible.
The Bible is a collection of books and letters that were authored at different times in history. However, God is depicted as having the same message, while the people are described as not listening to the message. Meaning, the people are often made to look like fools, with the exception of a few characters who understand God's message and live accordingly.
God's message in the Bible is this:
Disobeying God is bad – so bad that it deserves death because it opposes the giver of life; God asks people to stop sinning or else the natural consequence is death; People continue to do bad things (like kill others, assaulting others, stealing, etc.) and this makes God very angry, because God does not want people to hurt you, nor does he want you to hurt others; God warns people to return to obeying him or else they will die; God promises people that if they return to obeying him, he will forgive them; however, God says that forgiveness is not easy – sin deserves death, so something has to die to pay the price for sin; God tells people to sacrifice animals, but animal deaths do not truly rid people of sins; God enters into a human body, and "dies" to cover the sins of all people; however, his message still does not change – return to obeying me, or you will die from your sins. The only difference is that now salvation is possible (Matthew 19:25-26) because God's death has paid the price for our sins, so when we return to obeying God it is as if we had never disobeyed (Romans 3:25; 2 Peter 1:9)
All this happens over the course of thousands of years, but the message stays the same. Oftentimes, people are described as not understanding the message, yet it still remains the same.
Now, let's consider other witnesses.
Consider that about 600 years after this final event, where God "dies" for people to remove their sins, another man claims to have interacted with God. However, this new man's message is much different – his message is to kill those who are unbelieving.
Really, this second message sounds kind of similar, except that it's a twisted version of the original message that has been consistent for thousands of years.
Whereas the message of the Bible is that God hates evil (killing, stealing, assaulting others, etc.) and that the consequence of these actions is death, the message of this person who comes 600 years later is that people should take joy in killing those who refuse to believe. In fact, according to this new man, it is a form of worship to kill those who choose not to believe in God.
This was Paul's error. He too believed that he was worshiping God by killing Christians, until he came face-to-face with Jesus Christ (Acts 9). And actually, it is Jesus Christ who warned this would happen saying, "Yes, the time comes that whoever kills you will think that he offers service to God." (John 16:2 WEB)
Rather than unbelievers killing the believer, this last man says that believers should kill the unbelievers - again a twisted version of the original message.
In addition to this twisted message, this new man also says it is not enough to believe in a God only. According to this man, people have to adopt the exact faith of this last man in order to be considered believers, even though this set of beliefs is quite different from the other 39 witnesses of the Bible who communicated the same message over the course of roughly 1,500 years.
This man who comes 600 years later is the founder of Islam.
Remember that car accident we were discussing?
Imagine if 39 people saw the car accident happen and all agree about how it happened, then someone else comes late and communicates a twisted version of the story. Who do you believe? Keep in mind that ALL of these people are strangers to you.
No one is alive today who has met any of these people in the Bible, including the one who came 600 years late.
For some people, this series of questions will lead them to realize that it is reasonable that God exists. However, others may have still more questions about God that need to be answered in order for them to believe.
Many people are comfortable with their current beliefs, so they are unwilling to consider a new belief system. To them, belief is how they want to view the world, instead of learning what is true about the world. For Christians, we know that the Bible teaches about the truth of the world. We also know that anyone who refused to return to God will be doomed to an eternal death (Revelation 2:11).
Many people are unwilling to believe simply because they are unaware of what is true. Instead, they choose to believe what is most convenient for them, unaware that one day they will come face-to-face with what is true whether the want to or not.
"For the time will come when they will not listen to the sound doctrine..." (2 Timothy 4:3 WEB)