Asch's Paul is the brilliantly dynamic prophet and organizer of the early Christian Church. He was driven by an ineluctable faith, by visions no less intense. No danger stopped him. But St. Paul was not only an evangelist. He was pugnacious and something of a politician. Says Novelist Asch: "The center of his world was his 'I' . . . which measured, judged and defined." Paul lacked that "soft, winning goodness, that graciousness of speech, that warmth which characterized his fellow apostle, Peter." On the contrary, he was hard and ascetic. He was also epileptic, and saw many a vision even before he fell to earth blinded by the Light which burst upon him on the Damascus road when the voice of Jesus spoke to him and converted him.
All his life thereafter Paul strove "to fuse into one person . . . the two Pauls, Paul the Jew and Paul the Greek." He was considered a heretic by his Jewish brethren not because he believed that Jesus was the Messiah, but because he believed that He was the Son of God. And all through his life Paul never quite lost the feeling that, while he meant to reconcile the world to Jesus, he had actually "thrust a wedge between Israel and the world."
Pageantry, Paganism, Piety. The Apostle is packed with realistic resuscitations of First-Century life in the Roman Empire, elaborately drawn portraits of famed pagans (Emperor Caligula, Empress Poppaea, Philosopher-Statesman Seneca), vivid descriptions of the burning of Rome, Nero's persecutions, the mystery cults and the worship of Diana.
For Novelist Asch, the long years that went into the writing of The Nazarene and The Apostle were a dedication. On the last page of The Apostle he wrote: "I thank Thee and praise Thee, Lord of the world, that Thou hast given me the strength to withstand all temptations and overcome all obstacles . . . and to complete the two works."
---from Time.com

Asch's story deals minutely with the struggle between the Jews and Christians to decide if Christ was the expected Messiah, and whether, in ministering to the gentiles, the law of Torah should be enforced upon them, or abrogated to some extent (and if abrogated, to what extent?).
Paul believed that the gentiles should be given the salvation of Christ just by faith and left uncircumsized and eating pork if they so chose.
Most of the book flowed like a novel should, but it had some longueurs, when Asch discoursed on the finer points of the Torah or you could tell he was just reiterated the letters of Saint Paul from the New Testament itself.
Nero burns Rome and sacrificies Christians in the arena and Seneca and Petronius are also portrayed here, as well as a good deal about Saint Peter. It definitely has its exciting moments. Many are martyred and St. Peter is famously nailed to the cross upsidedown.
Most interesting to me, while reading this 754 page tome, was wondering what happened to Asch to make him write the trilogy of Christian-themed books and alienate most of his Yiddish readers. Did he convert?
In the book they recommend that Jews accept Jesus and hold to the laws of the Torah as well. I think he must have been like that, but this is mere speculation, of course.