For another thing there is no one else to corroborate and interrogate the issues and personalities of the New Testament, except for Jewish sources who wrote generations later.
Josephus was born of priestly descent around 37 c.e., but his curiosity led him in early life to experiment with diverse and even countercultural Jewish expressions. First, he tried the philosophy of the Essenes. Though he was favorably impressed with them, he left them. Then he joined up with an ascetic wilderness group led by a charismatic leader named Banus.
Perhaps this group exhibited something that Josephus found attractive among the Essenes. All these experiences came before the age of 19. Then he took up an interest in the Pharisees, another Jewish sect, though his later commentaries show that his involvement with them was strained.
A journey to Rome in 63 c.e. triggered a respect for the Roman Empire, one that became evident in his later actions. When he returned, war broke out between his countrymen and Rome, and Josephus reluctantly and futilely led a detachment of Galileans against the Roman army.
His troops were overwhelmed, and his surviving cohorts made a pact to die rather than surrender. Driven to the point of committing suicide, Josephus refused and fled. He presented himself to Vespasian, the Roman general, as an ally, translator, and guide.
He projected himself as another Jeremiah, the prophet who led his people at the time of the Babylonian invasion, through his preaching in Jerusalem against the uprising and through his prophecies about Vespasian and Roman destiny.
Josephus’s decision to side with Rome was motivated by religion as well as by an instinct for survival. However, he was considered a traitor by most of his Jewish fellows.
At the end of the campaign Josephus was honored in Rome with a country villa, special privileges, and friendship with the Roman emperor. He never returned to his home country, much less to his wife and family. He spent the rest of his days as a historian, writing at least four compositions.
The first was the Jewish War, an account of the events leading up to the difficulties of 70 c.e. Josephus blames the war on a small band of Jewish fanatics. The second is Against Apion, a defense of Jewish culture and historical pedigree.
The third is the longest, a history of the Jews from creation to his own time (around 90 c.e.), called Jewish Antiquities. This work is modeled after other Greco-Roman histories and skillfully combines secular and religious virtues in the telling of the Jewish story.
Finally, he writes his own Autobiography, largely as a defense for his conduct during the war. To the last of his sentences, however, he is an apologist for his Jewish people and their cause.
His histories are assessed as factual and fair. While he was in Rome he had access to official records and relied on other sources, like Nicolas of Damascus, a historian of Herod’s court. He had firsthand knowledge of the land, the personalities, the issues, and the battles.
Many of his own descriptions can serve as a background for such New Testament persons as the Herods, the priests, the Pharisees and Sadducees, John the Baptist, James ("brother" of Jesus), and perhaps of Jesus (Christ) of Nazareth. Jerome touted Josephus as the "Greek Livy" for his masterful history telling.
It is true that Josephus’s powerful voice has persuaded Christians over the ages about the historical veracity of their scripture. For this reason Josephus was preserved in Christian circles, not Jewish ones; in fact, in certain ancient manuscripts of the Bible, the writings of Josephus have also been appended.
But others question his neutrality and impartiality. There are inconsistencies in his descriptions of his leadership during the war and questions as to whether or not he supported the revolt from the beginning.