Paul begins his concluding remarks in chapter 13 by reminding the brethren that he will examine them, and that “by the mouth of two or three witnesses every word will be established.”
Throughout Scripture, God has always protected the innocence and integrity of good men by requiring multiple and credible witnesses before receiving an accusation against another. We find this in the Law of Moses in Deuteronomy 17:6, in the Law of Christ in Matthew 18:15-20, and in the writing of Paul in 1 Timothy 5:19.
Whether good or ill, a matter needs proper testimony and verification before it can be known and told. Jesus was accused of being His own witness in John 8:13. Jesus rejected that accusation, noting that though He did bear witness of Himself, the Father also bore corroborating witness (John 8:18). Earlier, Jesus had claimed two witnesses to Himself: John and the works that He himself had done all bore testimony to His claims (cf John :31-36).
The same may also be said of those who claim to be followers of Jesus. It is one thing to claim to be a Christian, it is another to have a corroborating witness. Who else is qualified to testify on behalf of the professed child of God?
Romans 8:16 answers this question for us: “The Spirit Himself bears witness with our spirit that we are children of God.” No one may rightly call himself a Christian (child of God) without the corroborating witness of the Holy Spirit.
But how does the Holy Spirit bear witness? The answer is, “In the doctrine of the New Testament.” In John 16:13, Jesus promised the apostles that they would be guided into all truth. The only way to make disciples is to preach the gospel to the lost and for the lost to respond to the gospel through faith and baptism (Matthew 28:19; Mark 16:15-16; Romans 1:16; 10:13-16).
Only those who have heard the Spirit-inspired gospel (2 Tim 3:15-17) and responded accordingly are Christians. Self-witness is insufficient. Human corroboration is irrelevant. The Holy Spirit is the only true witness to testify that we are the children of God. Therefore, it is incumbent upon us to examine ourselves, whether we be in the faith and prove our own selves (2 Cor 13:5).