In 2 Corinthians 11:3-4, Paul laments that the Corinthian Church may be falling too easily for worldly deceit, just as Eve was deceived by Satan. In verse 4, we read "For if he who comes preaches another Jesus whom we have not preached, or if you receive a different spirit which you have not received, or a different gospel which you have not accepted—you may well put up with it!" In this one verse, we see that not everyone who claims to be a Christian actually is, for there are three elements of Christianity that must be satisfied.
The first element is the Jesus whom Paul and the other Apostles preached. I often like to draw the analogy of a modern man claiming to be Jesus. Should this man gain followers, could those followers be called Christians?
It turns out, I no longer have to use this analogy hypothetically. I was not aware at the time I started using it, but I am now aware that people have been claiming to be Jesus for a long time. For example, Alan John Miller claims to be Jesus reincarnated, and even has a partner, Mary Suzanne Luck, who claims to be Mary Magdalene. But Jesus Himself warned that false Christs would go out into the world (Matthew 24:23-25), so obviously Miller is not Jesus. Therefore, his followers are not Christians.
If followers of real false Christs are not Christians, how much more should followers of imaginary Christs also be considered disqualified? The identity of Jesus is seen very clearly in the Scriptures. We can, for example, easily discount the Jehovah's Witness belief that Jesus did not rise bodily, because Christ Himself claimed He would raise His body (John 2:19-21).
The second element is the spirit which the Corinthians received. Christianity is unique among all religions, as it gradually regenerates and reforms the believer. Jesus said that His disciples would be known by their fruits (Matthew 7:20), and in Galatians 5:22-23, Paul gives us a helpful list of what the fruits of the Spirit are: love, joy, peace, longsuffering, kindness, goodness, faithfulness, gentleness, self-control. It goes without saying, therefore, that a hateful, miserable, violent, impatient, selfish, evil, blasphemous, brutal, and lawless religion is very much not Christian. Thus, given the reputation Westboro Baptist Church has built for itself, it is safe to say this particular church is a religion all to itself.
The third element of Christianity is the Gospel, which is arguably the most important element, as it encompasses the other two. So vital is the Gospel to Christianity that Paul actually pronounced a curse on anyone, man or angel, even himself, who would dare preach another Gospel (Galatians 1:8). But so many "denominations" preach false gospels. The Roman Catholic Church, for example, preaches a range of contradictory Gospels, ranging from "no salvation outside the Church" to claiming that those who never heard the Gospel can be saved (Catechism of the Catholic Church 847). Thus, we can discount Catholicism as Christianity.
These three elements, regardless of the testimony of a church or individual believers, are essential to the Christian faith. If anyone lacks one of these elements, their claims to be Christian are invalid, and on judgment day, they will hear the dreaded words "I never knew you" from the good Lord Himself. Let us therefore ensure that we know the Jesus, whom Paul preached, in the Spirit, whom we have received, and preach the Gospel, which we have accepted.