Question: How can you tell if someone is truly a Christian or not?  Are there things that demonstrate a person’s spiritual condition?  Also, if you see someone living a very immoral lifestyle, contrary to the Scriptures, is it wrong to assume they are not a Christian?  Or is that just judging?

My Answer: Good questions.  In a culture that is infatuated with “tolerance” and acceptance of every lifestyle and belief system, it seems harsh to state that any certain person is not a Christian.  Indeed, if you say that about someone, you very likely will be accused of being judgmental and mean-spirited.  As always, the Bible itself provides the best answers.

First of all, I must emphasize that only God sees the heart, and the final judgment of men’s souls is in His hands.  Also, we must keep in mind that all true Christians are in a process of growing spiritually.  We all make mistakes; we all sin.  In the process of sanctification, Christians stumble along the way.  Of course, this does not excuse any sin in a believer’s life.  But as C. S. Lewis said, “When a man who accepts the Christian doctrine lives unworthily of it, it is much clearer to say he is a bad Christian than to say he is not a Christian.”

However, the Scriptures do provide a number of characteristics that demonstrate people’s spiritual status.  In other words, you can tell if someone is a Christian by their behavior, their beliefs, and their testimony.  Their testimony?  Yes, Jesus taught we must be born again (John 3:7), and if a person is “in Christ” he is a new creation (2 Corinthians 5:17).  If a person is a true believer, then there is a testimony of a new birth and a transformative conversion experience.  A Christian is a new person, one who has been radically changed in his beliefs, behavior, morals, indeed his entire life.  The first evidence that someone is a true Christian is that they can testify to a changed life (see 1 John 5:10-12).

Now, as for people’s behavior and beliefs, the epistles of John address these matters in several passages.  John was dealing with people in the church who claimed to know Christ, but did not exhibit the hallmarks of a Christian life.  Consider a few examples concerning our behavior and lifestyle:

• 4 Whoever says “I know him” but does not keep his commandments is a liar, and the truth is not in him, 5 but whoever keeps his word, in him truly the love of God is perfected. By this we may know that we are in him: 6 whoever says he abides in him ought to walk in the same way in which he walked.  (1 John 2:4-6)

• If you know that he is righteous, you may be sure that everyone who practices righteousness has been born of him. (1 John 2:29)

I John 2:6-10 offers several insights here.  John tells us that the Christian is marked by a life dominated by righteous behavior, not sin (vv. 6-7, 9).  Someone who makes a “practice of sinning is of the devil” (v. 8).  It is the moral behavior of a person that distinguishes the child of God and the child of the devil (v. 10).

A word of explanation may be helpful here.  The passage in 1 John 2:6-10 does not mean that Christians never sin.  We all sin, as John himself stated (1 John 1:8).  But for the Christian, sin is not the habitual practice of his/her life.  As Alistair Begg once said, sin may be present in the life of a believer, but it does not reign.  Sinning is not the norm for a Christian.  But a non-Christian demonstrates a “practice of sinning” (verse 2:9 above).

• Beloved, do not imitate evil but imitate good. Whoever does good is from God; whoever does evil has not seen God (3 John 1:11).

The preeminent mark of a Christian is that he demonstrates a lifestyle motivated by love for God and love for people (see John 13:35).  Consider the following:

• 14 We know that we have passed out of death into life, because we love the brothers. Whoever does not love abides in death. 15 Everyone who hates his brother is a murderer, and you know that no murderer has eternal life abiding in him.  (1 John 3:14-15)

• 7 Beloved, let us love one another, for love is from God, and whoever loves has been born of God and knows God. 8 Anyone who does not love does not know God, because God is love. (1 John 4:7-8)

There are also passages that tell us that either wrong belief or unbelief indicates that a person is not a true follower of Christ.  Consider these examples:

• 22 Who is the liar but he who denies that Jesus is the Christ? This is the antichrist, he who denies the Father and the Son. 23 No one who denies the Son has the Father. Whoever confesses the Son has the Father also.  (1 John 2:22-23)

• Everyone who believes that Jesus is the Christ has been born of God… (1 John 5:1).

• Whoever has the Son has life; whoever does not have the Son of God does not have life (1 John 5:12).

• Everyone who goes on ahead and does not abide in the teaching of Christ, does not have God. Whoever abides in the teaching has both the Father and the Son (2 John 1:9).

Of course, John is not the only New Testament writer who says that there are ways you can tell the true believer from a non-Christian.  For example, Paul emphasizes that Christians will not live like people in the world.  Their lives are different (see Ephesians 4:17-24, Titus 2:11-13).  Peter noted that not only do Christians live differently, but people in world notice the difference and are perplexed by it (1 Peter 4:2-4).  Jesus himself said that “by their fruits you will know them” and it is the person who does the will of God who enters the kingdom (Matthew 7:20-21).  In Luke 6:43-45, Jesus again emphasizes the same idea.

Let’s summarize what we have seen in the Scripture.  The ultimate judgment of the condition of men’s souls is in God’s hands.  But there are behaviors and beliefs that do define what it means to be a Christian.  Therefore, for a person to reject Christ, to deny basic Christian doctrines, and to live in unbelief means that they are not a Christian.  At the same time, if a person’s life is immoral and ungodly, that is, habitual and willful sin is a hallmark of their life, then it is evident that this person is also not a Christian.  This is not “judging” but instead it is an honest assessment based on Scripture and the biblical definition of what a Christian is.