Paul told the Corinthians to "test yourselves to see if you are in the faith; examine yourselves!" (2Co 13:5). Did he perceive that there were some that were not aware they weren't believers, or did he suggest this knowing that the process would build their faith? How do you even know how to examine yourself? He had previously asked, "Are you not fleshly, and are you walking like mere men?" (1Co 3:3). They could be either worldly men or "spiritual men" (:1). If the latter, "he is a new creature; the old things passed away; behold, new things have come" (2Co 5:17). In this case Paul comments, "Do you not recognize this about yourselves, that Jesus Christ is in you?" (13:5). But regarding the first case he observes "unless indeed you fail the test?" (:5). Here it could be that the person "does not accept the things of the Spirit . . . [since] he cannot understand them, because they are spiritually appraised" (1Co 2:14). How difficult would it be to test yourself and decide? If you question excessively you may become like "the one who doubts [who] is like the surf of the sea" (Jas 1:6) and become like "a double-minded man, unstable in all his ways" (:8). It is possible to be both since Paul addressed them as "men of flesh . . . [as well as] babes in Christ" (1Co 3:1). How do you determine from which part of your mind the current thought originates? "He who is spiritual appraises all things" (2:15).
If you are spiritual you "are His workmanship, created in Christ Jesus" (Eph 2:10). That should answer the test question "that Jesus Christ is in you" (2Co 13:5). Paul explains "it is no longer I who live, but Christ lives in me" (Gal 2:20). Paul does not mean that he has been "beamed up", because he refers to "the life which I now live in the flesh" (:20). It does mean "you have died [to yourself] and your life is hidden with Christ in God" (Col 3:3). He relates "in the flesh I live by faith in the Son of God" (Gal 2:20). "You have died with Christ to the elementary principles of the world" (Col 2:20). "If we died with Him, we shall also live with Him" (2Ti 2:11). "He made you alive together with Him, having forgiven us all our transgressions" (Col 2:13).
Peter instructed "like the Holy One who called you, be holy yourselves also in all your behavior" (1Pe 1:15). "In obedience to the truth [you] purified your souls" (:22). "Every one who has this hope fixed on Him purifies himself" (1Jn 3:3). "This is the will of God . . . that you abstain from sexual immorality; that each of you know how to possess his vessel in sanctification and honor" (1Th 4:3-4). "Do you not know that the unrighteous will not inherit the kingdom of God?" (1Co 6:9). "Therefore do not be partakers with them . . . [but] walk as children of light" (Eph 5:7-8). Paul told them they "received from us instruction as to how to walk and please God" (1Th 4:1). He said "let us cleanse ourselves from all defilement of flesh and spirit, perfecting holiness in the fear of God" (2Co 7:1). The goal is to have "clean hands and a pure heart" (Ps 24:4). "Therefore, if anyone cleanses himself from these things, he will be a vessel for honor, sanctified, useful to the Master, prepared for every good work" (2Ti 2:21). "The unbelieving husband is sanctified through his wife" (1Co 7:14). Women should "continue in faith and love and sanctify with self-restraint" (1Ti 2:15). Pursue peace with all men, and the sancification without which no man will see the Lord" (Heb 12:14). "He disciplines us for our good, that we may share His holiness" (:10).