2 Corinthians 13:3-6
3 Since ye seek a proof of Christ speaking in me, which to you-ward is not weak, but is mighty in you.
4 For though he was crucified through weakness, yet he liveth by the power of God. For we also are weak in him, but we shall live with him by the power of God toward you.
5 Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates?
6 But I trust that ye shall know that we are not reprobates.
Abridged Commentary - 2 Corinthians 13:5
13:5 The Apostle Paul responds to the Corinthians' seeking "proof of Christ speaking in (him)" (verse 3) with an instruction to examine themselves, as they are the credentials of the fact that he is a true teacher, being his very own converts (1 Corinthians 4:15, 15:1-2: 2 Corinthians 1:19).
Charles Bing - Grace, Salvation, and Discipleship - Examine Yourselves, 2 Corinthians 13:5
(Salvation) Interpretation: Professing Christians are encouraged to examine themselves to see if they really are Christians.
(Discipleship) Interpretation: The Corinthian Christians are told to look at their own salvation as a testimony to Paul's authenticity as an apostle because he preached the message that saved them.
One of the consequences of having a performance-based salvation is that assurance of salvation is not based on faith in Jesus Christ alone but on one's commitment, works, or faithfulness. This alone invites introspection. The problem is that there is no biblical exhortation to examine our own salvation - unless we use this passage, as many do. On the contrary, the New Testament is full of claims, statements, and assumptions that the authors and their readers are undoubtedly saved.
"But doubts are good," it is claimed. "We should all question our behavior to see if we are really saved." But is that a healthy approach to the Christian life? I think we should all question our beliefs about Jesus Christ, His person, His work, and His Promise, to make sure the object of our faith is true. But others say we should focus on ourselves instead. Have we really believed? Are we behaving like a Christian should or would?
The (Salvation) significance of this passage is that it gives explicit permission, even directive, to question the authenticity of our salvation. Taken in isolation from the context, that is what this verse seems to say. But context changes everything.
We have to start with the purpose of the epistle. Paul is writing to the Corinthian church which had its moral problems, but was also questioning the authenticity of Paul's apostleship. Not that they always had doubted him, but false apostles had influenced them against Paul (2 Corinthians 10:2). So in the midst of correcting their moral issues, he also defends his apostleship (2 Corinthians 5:12-13; 10:1-11:33; 12:11-33).
In spite of their immorality and the Corinthians' doubts about him, Paul affirms their salvation. In fact, his appeals to them are based on that fact that they are believers (2 Corinthians 1:21-22; 3:2-3; 6:14; 8:9; 13:11-14). Paul had no doubt they were saved - he led them o Christ (1 Cor. 15:1-2: 2 Cor. 1:19). And that fact forms the climax of his argument for his own authenticity. He considers the saved Corinthians his credentials of authenticity (2 Cor. 3:1-3). He says in 10:7, "If you are Christ's, then we are Christ's." In other words, if Christ is in them, then he also belongs to Christ, because he brought them the gospel that saved them.
So in chapter 13, we see the Corinthians wanted proof that Paul is a genuine spokesman for Jesus Christ (v. 3). Paul resorts again to the argument that they themselves are his credentials of authenticity. After inviting them to self-examination, he asks, "Do you not know yourselves, that Jesus Christ is in you? - unless indeed you are disqualified." It is a rhetorical question tinged with irony. Rhetorical because they know the answer - Yes, they are in the faith (the truth of Christ, not personal faith) and Christ is in them. Ironical because they want to examine Paul but he turns it around telling them the answer is in them, not him. Since they are saved, he is an authentic apostle of Jesus Christ, because he is the one who preached Christ to them! Only if they failed the test (from adokimos, "are disqualified"), would he also. What are they disqualified from or what test might they fail? It may be that Paul is not referring to their (or his) eternal salvation per se, but the failure to live up to the truthfulness of the faith in Christ that they claim. In other words, they would fail to live faithfully as the gospel demands. This ethical concern is certainly prevalent in the context (vv. 4, 7, 8). Just as Paul has been consistent with his claim to be an apostle (vv. 7-8), they should pass the same test of living up to what they claim they are.
In my opinion, never has a passage been so carelessly yanked out of context and used to do immeasurable damage to God's people. Doubt does not grow disciples of Jesus Christ. You can't go forward if you are always looking backward. Did I believe enough? Do I behave good enough? These questions are subjective and slippery. The only legitimate question is an objective one: Do I believe in Jesus Christ as the Son of God who died and rose for me and guarantees me eternal salvation? This passage does not invite examination of behavior anyway - it invites them to look at what they believe; "as to whether you are in the faith" refers to objective Christian truth.
Self-examination would produce doubts in any honest person who is less than perfect. But God does not want us to doubt His acceptance of us in His family. On the contrary, the assurance of His love and acceptance is His main motivation for us to love and serve Him in return.
To know if you are saved, keep your eyes off yourself and keep them on Christ!