Paul begins this epistle, as many others, by affirming his apostolic office. Because he is an apostle he is qualified to minister to the churches and furthermore to write to them under inspiration so that they must give the greatest possible attention to his words.
It is one thing to be self-effacing when men attack us personally; it is quite another thing to fail to defend the work of God. Paul was not an oversensitive, defensive person, but he knew that his apostolic authority must be defended for the sake of the gospel. Let pastors, elders and deacons not make the mistake of letting a false humility prevent them holding high the office into which God has called them.
Every minister is called to defend the church of God against error. He must therefore be vigilant and rise to the occasion when the doctrine of Christ is under attack. He cannot carry on regardless teaching what interests him, without considering the current battles that the church is facing.
Paul was appointed an apostle not by man but by Jesus Christ. How is it that Christ is put in a category of beings that does not include ‘man’? Paul certainly knew that Jesus had been born, had lived, and had died a true man, and that he had human brothers (Galatians 1:19), and yet the authority with which he acted in sending Paul was nothing less than divine authority. Because Paul accepted the divine person of the Lord Jesus Christ, he could therefore say that God had appointed him to this office not man.