On what basis can Paul's apostolic authority be justified?
The most significant validation of Paul’s apostleship comes from the apostle Peter. In 2 Peter 3:1-2 we read,
This is now, beloved, the second letter I am writing to you in which I am stirring up your sincere mind by way of reminder, that you should remember the words spoken beforehand by the holy prophets and the commandment of the Lord and Savior spoken by your apostles. (NASB) 2 Peter 3:1-2
Peter says that he wrote this book to remind us of the words spoken by the holy prophets and the commandments of the Lord as spoken by the apostles. Then he continues talking about future things written by prophets of old. Finally, he concludes the section by referring to Paul. He now says that Paul wrote scripture also (2 Peter 3:15-17). In fact, Peter says that Paul wrote some things that are hard to understand. Peter included Paul along with the prophets and apostles.
It is clear that Paul is an apostle when we read his letters and realize the oother apostles accepted the very letters Paul wrote in which he states repeatedly that he was an apostle in the opening verse of many of them,
|Romans 1:1||Paul, a bondservant of Christ Jesus, called as an apostle, set apart for the gospel of God. (NASB)|
|1 Corinthians 1:1||Paul, called as an apostle of Jesus Christ by the will of God, and Sosthenes our brother. (NASB)|
|2 Corinthians 1:1||Paul, an apostle of Christ Jesus by the will of God, and Timothy our brother, to the church of God which is at Corinth with all the saints who are throughout Achaia. (NASB)|
|Galatians 1:1||Paul, an apostle (not sent from men, nor through the agency of man, but through Jesus Christ, and God the Father, who raised Him from the dead). (NASB)|
|Ephesians 1:1||Paul, an apostle of Christ Jesus by the will of God, to the saints who are at Ephesus, and who are faithful in Christ Jesus. (NASB)|
|Colossians 1:1||Paul, an apostle of Jesus Christ by the will of God, and Timothy our brother. (NASB)|
|1 Timothy 1:1||Paul, an apostle of Christ Jesus according to the commandment of God our Savior, and of Christ Jesus, who is our hope. (NASB)|
|2 Timothy 1:1||Paul, an apostle of Christ Jesus by the will of God, according to the promise of life in Christ Jesus. (NASB)|
|Titus 1:1||Paul, a bondservant of God, and an apostle of Jesus Christ, for the faith of those chosen of God and the knowledge of the truth which is according to godliness. (NASB)|
Paul was an apostle because the Holy Spirit repeatedly said he was.