A Christian can be defined as a person who has, by faith, received and fully trusted in Jesus Christ as the only Savior from sin (John 3:16; Acts 16:31; Ephesians 2:8–9). And in the heart of the Christian resides the Spirit of Christ (Ephesians 3:17; 1 Corinthians 6:19; Romans 8:11). Now, “if anyone does not have the Spirit of Christ, he does not belong to Christ” (Romans 8:9), and this person, then, is not a Christian. Thus, the term “fake Christian” is a misnomer. You are a Christian or you are not a Christian; one is either with God or against God (Matthew 12:30).
That being said, this question is certainly a legitimate one in the minds of many people. And this is likely due to the behavior of some Christians; however, it is also likely because of the behavior of many who think they are Christians or profess to be Christians, but who are not. The reasons many believe they are true Christians when they are not are many and varied. False teaching is certainly one reason. When churches eschew teaching sound doctrine, the end result will be congregants who do not know the truth of God’s Word. How can they keep in step with the Spirit, when the Truth is not in them?
Also, some believe their recitation of a prayer or responding to an “altar call” alone may have turned them into a Christian. Many believe their religious traditions, such as being baptized as an infant, secured a spot in heaven for them, or that their plentiful good works alone have put them in good standing with God. And, of course, some believe church attendance alone guarantees salvation. The point is that many who profess to be Christians are not Christians at all. Yet they complacently remain convinced that all is well with their soul. Sadly, many will live their entire lives believing they were Christians only to one day hear these words from Jesus Christ: “I never knew you. Away from me, you evildoers!” (Matthew 7:23).
The clear teaching of the Bible is that when someone is saved his life will most definitely change as he is a “new creation, the old has gone and the new has come” (2 Corinthians 5:17). A true, born-again Christian will strive to bring glory and honor to Christ by living a life that is pleasing to God (1 Peter 1:15–16; 4:1–4). True saving faith will indeed produce works or “fruit” in the life of the believer (James 2:17, 26). Thus, if there are no works of love in one’s life, a careful self-examination is certainly called for. The apostle Paul instructed those in Corinth to do this very thing: “Examine yourselves to see whether you are in the faith; test yourselves. Do you not realize that Christ Jesus is in you – unless, of course, you fail the test?” (2 Corinthians 13:5). Indeed, any profession of faith that does not result in a changed life and good works is a false profession, and the professor is not a Christian.
Now, even though the lifestyle of true Christians does reflect the presence of Christ in their hearts, we know we are not perfect. Christians do sin, and the apostle John makes it clear that we deceive ourselves if we think otherwise (1 John 1:8). And when Christians do sin, there are those eager to use their “slip-up” to further denigrate the true body of believers. That is why Paul admonished the church in Thessalonica to abstain from even the appearance of evil (1 Thessalonians 5:22) and to live in such a way as to “win the respect of outsiders” (1 Thessalonians 4:12).
What Christians will not do, however, is engage in repeated or habitual sin (1 John 3:6). One who engages in deliberate and habitual sin is simply proving that he does not know Christ and therefore cannot be abiding in Him even though he may live his life under the vast umbrella of religion and is thought, therefore, by many to be a Christian.
As believers mature in their faith, they will exhibit more and more evidence of their true Christian nature, such as their love for God, repentance from sin, separation from the world, spiritual growth, and obedient living. As Paul told the Romans, the genuine child of God has been set free from sin and has become a slave to God, and the result is eternal life (Romans 6:22).
We know that a true Christian or a person of true faith may “wander” from the faith like King David did when he committed adultery with Bathsheba and planned the murder of the woman’s husband. Adultery and murder are, most certainly, serious sins‼️‼️ But a real believer will ALWAYS repent and return because God promises to never lose any who belong to him. A false believer will never truly repent. For example, false believer Judas and Esau both “appeared” to repent for mistakes made but the Bible makes it clear their sorrow was only shallow
Your theory of the "Christian" identifty is interesting. Apparently your perspective is driven by a particular denominational philosophy and theological spectrum. Though many have contributed very meaningfully to your topic, I would like add that Christianity constitues plural denominational and theological models. Which means that our biblical exegesis and hermeneutics are colored by the denominational and theological underpinnings we were nurtured under.
Accordingly, Catholic, orthodox, protestant s (large bloc of many denominations), pentecostal, charismatic, etc., have divergent notions of biblical doctrines of sin, salvation, eschatology, pneumatology, and the many -isms in contemporary Christian worldviews. Consequently, while one particular theory of "true" Christianity may serve its proponents, other Christians may disagree with that designation - and validly so - because their philosophy sees it differently. For instance, regarding sin, in the academic systematic theology, you will notice gazillions of Christian theories of the nature of sin, etc. The matter is multifaceted and goes beyond just using a particular Bible verse to brand a person as "sinner" based on a subjective theological perspective. But these matters are denomination-specific. In my own experience, I grew up in a Pentecostal family with an extreme theory of sin that judged everything from dressing, dietary preferences, beverage choices, modern technology, and fashion choices/cosmetics as "sinful." Under that Pentecostal model, Bible verses were used to condemn innocent believers as "sinners" or "worldly" or "fake" or "backsliders" etc. But I moved far away from that fundamentalist theology because it portrayed God as anti-everything good that humans find pleasure in. To recap, no individual Christian theological perspective has the final word on the meaning of biblical doctrines, themes, concepts, or precepts. What one denomination or theological school of thought deems "sin" may amount to nothing in the lens of another equally credible Christian perspective.
Those interested in exploring "sin' perspectives more may check out these:
I do not necessarily endorse all the views in those web links, but just using them to show how extensive and complex the doctrine of sin is among the vast spectra of Christianity.
