I hear Muslims make this false assertion frequently. They erroneously argue that Paul came in after the real Apostles and took over corrupting Christianity with new foreign teachings. The truth is the evidence shows Paul was accepted by the original Apostles and the earliest Christians as a genuine convert with sound theology who was given an important mission from Christ himself.
The Historical Case for Paul’s Apostleship: And a Critique of Muslim Arguments
The use of the word apostolos is almost completely confined to New Testament writings. It is evident from Paul’s writings, that there were “apostles before [Paul],” going back at least to the resurrection appearances of Jesus in Jerusalem and elsewhere in Palestine. The appearance of the apostle vocabulary in the Gospel of Mark makes it likely that the notion of the apostle must be taken back into the Gospel story.
Jesus, followed by Paul and other early church leaders, appear to have been influenced in their use of the word apostle by the Jewish notion of the šālîaḥ who in late Judaism represented persons and institutions to others. While it is clear that nontechnical use of “apostle” by Paul resembles the secular šālîaḥ of later Jewish writings, the technical, or “solemn,” use of this word takes on a special character from the unique circumstances associated with the rise of early Christianity.
Galatians, Romans and the two Corinthian letters reflect the rise of opposition to the recognition of Paul as an apostle of Christ. While some of this opposition arose at a local level over personal criticism of Paul, by far the greatest rejection of his apostleship arose from the Judaizers, who at best sought to classify him as a humble šālîaḥ of the Jerusalem church.
Paul himself sought to establish the limited extent of the numbers of apostles. His careful words that Christ “appeared to me last of all” (1 Cor 15:8) serve to show that while there were apostles before him, there were no apostles after him. According to Paul he is both “the least” and “the last” of the apostles.
There should be no doubt that Paul based his claim to be an apostle on having seen the risen Lord and having been commissioned by him to go to the Gentiles (1 Cor 9:1; 15:8; Gal 1:11–17). To be sure, he pointed to his effectiveness in establishing churches, his own sufferings as a continuation in history of the sufferings of Christ and to his own integrity, but these served only to legitimize a ministry which had its basis in Christ’s confronting him on the road to Damascus.
Paul was a man of three worlds: Jewish, Greek, and Roman. Though he had been educated in the strictest Jewish tradition and had studied under the famous rabbi Gamaliel in Jerusalem, Paul spoke Greek fluently and was familiar with Greek thought and literature. He could express the doctrines and teachings of Jesus, many of which were based on Old Testament beliefs completely foreign to the Gentiles, in ways their pagan minds could grasp. In addition, Paul was a Roman citizen, which gave him special freedom of movement, protection in his travels, and access to the higher levels of society. It would be difficult to find a better choice of apostle to the gentiles than Paul.
And wherever he went Paul spread the "good news" of the Gospel he had first heard Stephen testify to before his stoning. That the law of God was given for a time to convince men of their inability to fulfill the will of God and to leave them with no option except to embrace the good news of Jesus Christ's death and resurrection. That was strong medicine for Judaism. The authorities wanted no part of it nor did some early Palestinian Judaizer converts.
But for such a one as Paul, the title apostle or "sent one" was never more appropriate. Paul made a series of trips throughout Asia Minor (today's Turkey) and Greece preaching Jesus as the Christ and planting churches of Gentile believers. Paul's converts were a mixed lot. A few of them were from honorable backgrounds, but the majority were pagans with sordid pasts (e.g. sexually immoral, idolaters, adulterers, prostitutes, thieves, greedy, drunkards, slanderers, swindlers, etc...). But Paul showed them how to be "washed," "sanctified," and "justified" through Jesus Christ and the Spirit of God to live a moral godly life pleasing to God.
And Paul's task of carrying the gospel of Jesus to the Gentiles was difficult for the gentile world was steeped in wicked occultic false religious systems. Paul encountered pagans who whorshipped a pantheon of Greek gods adopted and renamed by the Romans everywhere he went in addition to mystery fertility cults and indigenous animism.
But Paul had the competency to engage them. His experience with paganism originated locally with people groups like the Canaanites whom the Jews had separated themselves from. Look at Leviticus 19:19 the prohibition given forbidding the Israelites engaging in the fertility cult practices of the pagan Canaanites. The Canaanites believed in occultist sympathetic magic, the idea that symbolic actions can influence pagan gods and nature. Mixing animal breeds, seeds, or materials was thought to “marry” them” so as magically to produce “offspring,” that is, agricultural bounty in the future.
The Canaanites also sacrificed their children by roasting them on bronze altars to pagan gods. Sodom and Gomorrah were in Canaan. The Canaanites practiced incest, homosexuality, zoophilia, pedophilia, and burned their children as sacrifices all in the name of their gods. It was a very sexually immoral and wicked ancient nation and Jewish law was designed to keep them apart from the debauchery.
Paul was simply encountering more of the same as he traveled the dark pagan world of his era with the gospel seed as perhaps the most important apostle of the New Testament.