On that day many will say to Me, “Lord, Lord, did we not prophesy in Your name,and cast out demons in Your name, and do many mighty works in Your name?” And then I will declare to them, “I never knew you; depart from me, you workers of lawlessness.” –Matthew 7:22-23 [ESV]
Certainly there are people who think they are Christians who are not. There are a variety of reasons for such belief, but my experience is that it is especially pervasive in the area of cultural Christianity. Here in Albania, for example, Roman Catholicism, Orthodoxy and Islam intersect. Those who grow up in families associated with the first two views see themselves as Christians because, after all, they aren’t Muslims. But one’s Christianity is not determined by the family in to which he is born, but by the family into which he is born again. The second birth occurs at the moment of faith alone in Christ alone. God calls all—people from Muslim, Orthodox, Roman Catholic, Protestant, Buddhist, atheist, and all other backgrounds—to place their faith in the work of Christ and through that to be transferred by grace from the kingdom of darkness into the kingdom of light (Col. 1:13-14). Those who have placed their faith in Jesus Christ alone for salvation should think they are Christians because they are. “To all who did receive Him, who believed in His name, He gave the right to become children of God” (Jn. 1:12).
Those who place their faith in Christ should count themselves as children of God because God declares this to be the only requirement in order to receive the gift of salvation in His infallible word. Most of Christianity agrees with this essential truth, but the unity quickly fades in its application. One area where disagreement exists is in the area of assurance. The “free grace” segment of Christianity points to the finished work of Christ as declared in the Bible as the basis for assurance. “Believe on the Lord Jesus Christ and you will be saved” (Acts 16:31). If you have believed, you are saved. On the other hand, the “lordship” segment of Christianity declares assurance to be both a “reward of tested and proven faith” and a “subjective feeling.” Since the reward comes as a result of satisfactorily living the Christian life, a Christian can neither have assurance at the moment of faith alone in Christ alone nor can he depend on God’s word to know for certain that he is in Christ.
Matthew 7:22-23 is an oft-quoted passage used to make the case for false assurance. Teachers from the “lordship” section of the Christian spectrum declare that Jesus is here condemning false believers. A false believer is something like a person who has faith in Jesus but not “genuine” or “true” faith. A person can recognize the legitimacy of his faith by how it manifests itself in his life. The folks in Matthew 7 declare, “Lord, Lord,” but Jesus proclaims, “I never knew you!” They, therefore, had a false assurance that they would be counted right before God.
The folks, who were actually false prophets (Matt. 7:15-23 is one complete thought), did indeed have a false assurance, but the assurance was the result of having genuine faith in the wrong thing, namely, their works. When they come before the Savior, the false prophets do not point to Jesus as the basis of their salvation, but to their actions: “Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?” They believed that their good works justified them. Jesus replies: No!
Those who trust in their works as proof of their faith walk down the same dangerous path as the false prophets in Matthew 7. God has an extremely high standard for His children, but not even the Apostle Paul was so bold as to declare that he always met God’s standard (Phil. 3:12); instead, he strived to live a life that matched the approval he had from God in Christ. Jesus Christ has perfectly met God’s standard: He died for the sins of the world, and He offers all eternal life by simply trusting that what He accomplished for them is enough. Believers should wrestle with sin and count all as loss because of the surpassing greatness of what we possess in Christ because, indeed, we know we possess it. God tells us we do! And we will give an account of what we have done with the blessings God has given us, but not for entrance into eternal life with God. For entrance into His kingdom, we need only respond, “Lord, Lord, didn’t You die for me?” Yes!
 John MacArthur, “A Believer’s Assurance: A Practical Guide to Victory Over Doubt,” gty.org.
 See, for example, John MacArthur, “A Believer’s Assurance: A Practical Guide to Victory Over Doubt,” and “True Faith and True Grace.” gty.org. Perhaps the two other most popular passages are James 2 and Hebrews 6.