The primary sources for the life of Jesus Christ are Matthew, Mark, Luke, and John (Lea, 86). Very few secondary sources exist to talk about the life of Jesus Christ among contemporaries of early first century Christianity, and some of the sources that do exist could be argued to have been sources that in later copies Christians interpolated the text (Lea, 86). Regardless of the problems that concern the secondary sources, the Roman historian Tacitus shows record of the death of Jesus, Pliny wrote in the beginning of the second century that Christians sang about Christ as God, Lucian described Jesus as being a law giver and sophist, but Josephus describes Jesus as having done surprising things (Lea, 86). Of all the historical accounts of Jesus outside of the gospels many of them could have perhaps hypothetically been added to the text of the historians when the Roman Empire adopted Christianity as the state religion, but what is certain is that the gospels plainly talk about Jesus without any error or deception.
The Gospel of Thomas has sayings of Jesus, and Luke indicated a written record that he used to write his gospel from (Lea, 87). Lea appears speculative that the Gospel of Thomas was utilized in Luke’s work as Lea describes soon after the problem of various texts being produced to describe the life of Christ and other such people as he condemns these non gospel works as falsehood (Lea, 87). Overall, the gospel accounts about Jesus are certain, the Roman historians are not useful for saying much about Jesus but they may be useful for finding dates for the ministry, life, death, and resurrection of Jesus through allowing for the creation of a timeline that could place Jesus earthly person, and worst of all is that the non gospel non historical works written about Jesus may not account for much.
According to Lea, the birth of Christ can be estimated by the occurrence of three main historic events listed in the scripture, and these are the events of the death of Herod the Great, a census ordered by Augustus when Quirinius was governor of Syria, and the star of Bethlehem that lead the wise men into Jerusalem (Lea, 95). What is exciting about the three main occurrences listed that landmark the birth of Christ is that ideally one would have been recorded on a Jewish lunar calendar, another would have been recorded on the Greco-Roman calendar, and one would have been recorded forever astronomically by the heavens. All three events can thus be added together like a puzzle in order to locate the time of the birth of Christ within the calendar window of 6 or 5 B.C. (Lea, 96).
The later years of the ministry of John the Baptist are marked by various political people mentioned in the Bible as noted in Luke 3:1-2 (Lea, 96), and the fact that the ministry of Jesus began shortly after that of John tells us something about the date of the start of the ministry of Jesus Christ. The chronological information obtained from Luke regarding Tiberius succeeding the throne after Augustus died in A.D. 14 can help develop the timing of Jesus baptism in A.D. 26 or 27 (Lea, 97). Overall, from the time of the baptism of Jesus until his death indication that three Passovers took place occurs in the scripture, and this would place the date of the death of Jesus Christ at A.D. 29 or 30 (Lea, 97).
Regardless of what some scholars might think, historically accurate information about Jesus beyond what the gospels have to say might not account for very much. If historians that actually saw or had been associated with the message of Christianity during early Christianity did not believe in Jesus Christ, then certainly that says a lot about history in its ability to communicate truths about God. More seriously however is the fact that the birth, death, ministry, and resurrection are mainly important in the fact that they happened and not in the fact that they happened at a particular exact time. What I am saying is that the patterns of history that the Bible teaches are more important than the exact way and the exact time that those patterns came to pass for the most part unless the scripture makes a point to describe things a certain way. Overall, Paul the Apostle of Christ made clear that he was opposed to preaching a gospel that composed of human wisdom because it would mean that the cross would be emptied of its power (1 Corinthians 1:17), so Christians as a result should rely upon the power of God for preaching the gospel instead of on the wisdom of man to prove that some person named Jesus died on a certain time in a certain place a long time ago on a cross.
Lea, Thomas, and David Alan Black. The New Testament: Its Background and Message, 2nd ed. Nashville, Tennessee: H&B Academic, 2003.