From other references we understand that two qualifications needed to be met in order to be an apostle. First of all, he had to have seen the Lord. From Acts 1 we see that an apostle was to be a witness of the Lord during the days of His ministry from the time of the baptism of John until His death, resurrection, and ascension into heaven. The second qualification is that an apostle needed to be chosen specifically by Christ Himself. And in the case of Matthias, who replaced Judas, he was numbered among the apostles through the casting of lots, which was used to discern the Lord’s will in the selection.
This had created a problem for Paul because he was converted later. Paul had been around at the time of Jesus Christ, but he had not been one of the disciples who had followed Him throughout the days of His earthly ministry, and certainly not from the beginning with the baptism by John. Consequently, there were people who said that Paul really was not an apostle, that he was a person who had come along later and who had made claims to some special kind of revelation, and that all he was really teaching was the traditions of men and not the Gospel. So we read of occasions, particularly in Galatians, where Paul’s apostleship was under attack and he has to insist that he is an apostle.
In addition, the qualifications were also fulfilled in a slightly different way than had been spoken of in the earliest days of the church. Thus, Paul stresses again and again that he actually had seen the Lord. It is true that he had not been with Him all three years. But he had truly seen Him when the resurrected and ascended Christ appeared to Paul on the road to Damascus and appointed him as an apostle to the Gentiles. At the end of 1 Corinthians 9:2, Paul says that the Corinthians are proof of Paul’s apostolic ministry. They are the fruit of Paul’s labors.
Having demonstrated his apostleship, he now speaks in the second place of the rights of an apostle. He mentions two of them. One is the right to get married. He says that others of the apostles were married, and as they went around they brought their wives with them. The point Paul is making here is that even though he has a right to take a wife, he has foregone that right for the sake of the Gospel in order that he might be more effective as he traveled from place to place.
The second thing is the right to support. If Paul is spending all his time serving the churches through the preaching of the Gospel and in missionary work as he takes that Gospel to other places in the Roman world, he has the right to be supported by the Christian community. Apparently there were some who were challenging that idea, because he begins to talk about this right to support in a rather lengthy way. He brings forward a whole series of arguments in order to deal with this.

