New Defender's Study Bible Notes
13:5 Examine yourselves. Paul here reminds the Corinthians—and us—that it is quite possible for a man or woman to profess Christ and salvation, yet still be unsaved. They may even deceive themselves into thinking that such a profession has saved them. Therefore, we need to examine ourselves, to prove ourselves. The sure proof is the realization that Christ is indwelling us, by the Holy Spirit, resulting in godly lives and glad acceptance of all the revealed Word of God, as inspired by the same Holy Spirit.
13:5 reprobates. A “reprobate” is one who has been subjected to a proof test, and has failed. It does behoove anyone who is doubting and disobeying God’s Word to carefully examine the reality of His professed conversion to Christ. Every professing Christian needs to “give diligence to make your calling and election sure” (II Peter 1:10).