According to 1 Peter 3 : 15, Christians are commanded to always be prepared to make a defense to anyone who asks for a reason for the hope that is in us with gentleness and respect. In order to do this, followers of Jesus need to be prepared to answer two questions, “How do I know that Christianity is true?” and “How can I show that Christianity is true?”
For the Believer, the first question is more important, because as useful as apologetics can be, Christianity is primarily about a Person–Jesus, not just a set of facts about Jesus.
And this is eternal life, that they know you the only true God, and Jesus Christ whom you have sent. ~John 17:3
Christians do not believe merely because they are intellectually convinced that the claims of Christianity are true. That kind of belief would only put them on the same level as demons (see James 2:19). Christians have faith because they have had an encounter with the Spirit of God. They not only believe He exists, but they have experienced His presence, and trust in Him for their salvation.
This is not to say that showing Christianity to be true is without merit. Not only is it invaluable in removing intellectual barriers for those who have not consciously experienced God, it bolsters the faith of Christians in dry seasons of doubt. More importantly, we are commanded to show that Christianity is true by 1 Peter 3:15, as well as other passages of Scripture. While God is much bigger than human reason, He created us as thinking beings, equipping us to understand His creation. He provided us with senses and a brain to make sense of the world around us.
Jesus put it this way, Truly, truly, I say to you, we speak of what we know, and bear witness to what we have seen… If I have told you earthly things and you do not believe, how can you believe if I tell you heavenly things? ~John 3:11a, 12, ESV
C.S. Lewis wrote that we need good philosophy in order to answer bad philosophy. Many people make claims such as, “Christianity may work for you, but Buddhism works for me,” or “All religions are basically the same.” The truth is that all religions are superficially similar at best, and each one makes exclusive and competing truth claims. For example, Christianity claims that the problem is sin, and human beings cannot save themselves from sin, but need Jesus Christ to save them. Buddhism claims that the problem is suffering, but human beings can transcend suffering and achieve enlightenment through disciplines such as meditation. In Christianity, human beings are inescapably flawed and in need of a Savior; in Buddhism , human beings are capable of reaching enlightenment on their own through discipline. It is logically possible for both beliefs to be wrong, but it is not logically possible for both beliefs to be right.
A good place to start for examing the truth claims of one belief or another is First Principles. These principles were systematized by thinkers like Thomas Aquinas, but these are common sense principals that most people use every day whether they realize it or not..Humans are imperfect, and do not use these principles consistently, but just being aware of them and pondering them will help us become clearer thinkers. I will summarize them here, using the example of a dog (because I like dogs).
*The Principle of Identity*: The dog is a dog.
*The Principle of Non-contradiction*: The dog is a dog, and not anything other than a dog.
*The Principle of Excluded Middle*: It’s either a dog or not a dog.
*The Principle of Causality*: Something else caused the dog to exist (the only exception to this principle is God, who exists eternal and uncaused).
*The Principle of Finality*: Dogs exist for a reason.
While there is some debate about which principle is the most important, I side with those who say it is the Principle of Non-contradiction. Beliefs are either true or not true, and all the other principles logically follow from this. If two claims contradict and one is true, then the other is necessarily false. If Christianity is true that humans are unable to fix themselves, then Buddhism is not true on that point, and vice versa.
To show that Christianity is true, we should be able to demonstrate that it’s claims are consistent. The Holy Spirit can use the things we show the unbeliever to change their mind and draw them toward a divine encounter. The hope is that the unbeliever will not just know about God, but actually come to know God in an experiential way.