How to know Christianity is true

William Lane Craig is a gifted and highly intelligent Christian apologist. He has authored or edited over thirty books and almost two hundred articles published in professional philosophy and theology journals. In 2016, The Best Schools named William Lane Craig among the 50 most influential living philosophers.

I listened recently to some answers Craig gave in 2016 during a Q&A session at a church in Peoria, Illinois. Craig said he makes "a fundamental distinction between knowing Christianity to be true, and showing Christianity to be true" (27:10).  He said, "I think that the fundamental way in which we know Christianity is true is through the inner witness of the Holy Spirit." He quoted Romans 8:16 in making his case: "The Spirit Himself testifies with our spirit that we are God's children." 

I must say I am quite surprised William Lane Craig points to the Spirit's inner witness as the fundamental way he knows Christianity is true. I would have expected him to point to something objective and outside of himself as the primary source of salvation knowledge and Christian certainty, rather than to the personal experience of what the Holy Spirit is doing inside his soul. 

While the Third Person of the Trinity is certainly an objective reality, the inner witness of the Holy Spirit in the heart of a believer is by definition a subjective experience. It involves our perceptions and feelings that flow from the Holy Spirit's testimony within believers.  

Compare this holy experience of the Spirit's inner witness to the objective reality of Christ's death on the cross and the objective promise of the Gospel. Sanctification is a lifelong process the Lord produces inside a believer, involving of course many spiritual experiences. Justification, on the other hand, takes place the moment a sinner trusts Christ alone for salvation. Such trust relies upon the promises in God's Word and the glorious good news of the Gospel. 

Paul's single sentence in Romans about the Spirit's inner witness does not get presented until the eighth chapter of his monumental doctrinal treatise. If the Spirit's inner witness is indeed intended to serve as the foundation for a believer's certainty that Christianity is true, it seems extremely odd that the apostle did not highlight this spiritual experience throughout the earlier chapters where he meticulously spells out man's sin and God's amazing plan of salvation. 

Paul makes it clear in those earlier chapters that we as believers "have now been justified by Christ's blood" (Romans 5:9) and "we have been justified through faith" (Romans 5:1).  Paul knew for a fact that God "justifies the man who has faith in Jesus" (Romans 3:26).  This Gospel promise provides a believer with rock-solid assurance. The Holy Spirit grants us faith and emboldens our assurance as we rest upon the promises in God's objective and unchanging Word. 

And it is this knowledge and assurance of being saved by grace through faith (Ephesians 2:8,9) that actually enables Christians to be certain that Christianity is true. We have been given external confirmation in the promise of the Gospel. I know I am saved, justified, forgiven, and born again because of the Gospel promises in God's Word. The inner witness of the Holy Spirit certainly confirms my salvation, but this beautiful subjective experience is not presented in Scripture as the fundamental way for me to know I am saved and to know Christianity is true. 

Scripture contains plenty of God's thoughts about man, sin, salvation, eternity, etc. Such thoughts are certainly rational to God, and the rationality of these thoughts tends to be grasped by those who have been enlightened with what I call "sanctified reason." 

The Apostle John wrote: "You have an anointing from the Holy One, and all of you know the truth....the anointing you received from Him remains in you, and you do not need anyone to teach you. But as His anointing teaches you about all things and as that anointing is real, not counterfeit – just as it has taught you, remain in Him" (1 John 2:20,27).  The "Holy One" in this passage is Christ, and "the anointing" refers to the Holy Spirit. The Holy Spirit is the author of sanctified reason, and the body of every believer is "a temple of the Holy Spirit" (1 Cor. 6:19). 

Sanctified reason involves belief, knowledge, and spiritual insight into God's Word and His promises. It is a work of the Holy Spirit through the Word, and it comes about as the result of an "outer witness." The Gospel message is an outer witness delivered by the Holy Spirit that brings about justification when combined with faith, (Hebrews 4:2) whereas the inner witness of the Spirit is a subjective spiritual dynamic in the soul of a believer. 

Meanwhile, "The man without the Spirit does not accept the things that come from the Spirit of God, for they are foolishness to him and he cannot understand them, because they are spiritually discerned" (1 Cor. 2:14).  Spiritual discernment and sanctified reason are essentially the same things. The man who has the Holy Spirit living within him through faith in Christ is able to understand many things in Scripture. Believers receive sanctified reason through the new birth (John 3:7; 1 Peter 1:23) and through the Word of God (Matthew 4:4). 

"All Scripture is God-breathed," (2 Timothy 3:16) whereas our feelings and Christian experiences here on earth are still tainted at times with imperfect motives, mixed desires, and human weakness. And it is "the holy Scriptures which are able to make you wise for salvation through faith in Christ Jesus" (2 Tim. 3:15).  Once you are wise for salvation, you come to know for a fact that Christianity is true. By the way, if you would like some historical and mathematical reasons to have confidence in the message of the Bible, check out this article I wrote in 2013: "The Mathematical Proof for Christianity Is Irrefutable."

Historical evidence and other types of evidence for Christianity affirm the faith of a Christian and the truth of Christianity, but these things do not serve as the primary basis for the assurance of salvation. The Gospel alone has that kind of power. Believers can know for a fact that they are saved because God keeps His promises and the Lord's love and faithfulness are eternal.

Gospel power is greater than human intellect, human reasoning and rational arguments. The Holy Spirit works through the power of the Gospel to bring about the new birth, which brings with it sanctified reason and assurance. Spiritual conversion is a supernatural occurrence, and among other things, it lifts your human reason to a higher level.  Sanctified reason allows you to know things you would otherwise have no way of knowing or understanding (John 1:12,13). Sanctified reason enables believers to grasp what God did outside of us 2000 years ago at the cross to secure our salvation, and it also helps believers place full confidence in the Word of God.

At the same time, we cannot say that a professing Christian who has some doubts about his salvation or about the Bible must not be a genuine believer. D.L. Moody wisely said, "Faith is the root, and assurance is the flower." The object of our faith is even more important than the strength of our faith. Am I relying upon Christ's death as the payment for my sins, or am I trusting in my own efforts to save my soul? A believer's personal assurance of salvation grows stronger by meditating on God's promises, rather than relying upon his subjective personal experiences. 

Here are 3 key points to remember:

1. Your salvation was purchased outside of you on the cross where Jesus suffered and died for your sins. God invites you to look outside yourself to the cross and believe the good news of the Gospel.

2. The Holy Spirit is always at work inside believers, regardless of your particular feelings moment by moment.

3. While your feelings may be difficult to fully understand at times, you can always rely upon the fact that "it is impossible for God to lie" (Hebrews 6:18) and God never breaks a promise. (Joshua 21:45; John 3:16) Therefore, your salvation as a believer is secure. You have God's Word on it!

The Apostle John under the inspiration of the Holy Spirit taught people how to know if their religion was fake (1 John 2:4,9; 1 John 3:10,14,15), and how to know if they had eternal life. "I write these things to you who believe in the name of the Son of God so that you may know that you have eternal life" (1 John 5:13). This knowledge of eternal life through faith in Christ is what then confirms to a believer that Christianity is true.

This explains how I know Christianity is true. What about you? Are you trusting Christ alone for salvation? It is the only way to be forgiven of your sins, and the only way to receive the anointing and sanctified reason. This is how you can come to know that Christianity is true. Without the new birth, a person remains in spiritual darkness and only rises as high as his intellect and human reason can take him. 

So when all is said and done, which comes first: faith in Christ, or the knowledge that Christianity is true?

Faith in Christ comes first, which is a miracle of the Holy Spirit in the spirit of man. "Flesh gives birth to flesh, but the Spirit gives birth to spirit" (John 3:6).  Without saving faith, you only have human reason upon which to base your decision concerning the truthfulness of Christianity. You need to be raised up to a higher level in order to know for sure that Christianity is true.

Would you like to receive the forgiveness of sins as well as sanctified reason from your Creator? If so, "Repent and believe the good news" (Mark 1:15).  In those 6 words, Jesus presented man with the only path to Paradise. Are you on it? And if not, do you want to be on it?