While the historicity of the Gospels may be defended at a future point in time, I will focus on why the Gospels are really the only histories of Jesus that we have. Many wonder why no secular source wrote anything in detail about this supposedly amazing man. And I have the answer… They didn’t care. I’ve never heard anybody ask why the Romans never wrote much about Chinese history or vice versa, and then discredited theChinese for having written their own histories. In this way, the Christians wrote about Jesus while nobody else gave a hoot.
So maybe the only ones who did write accurately about it ended up having their biographies of Jesus being selected into what is called the New Testament today. What we have to realize is that what we call the “Gospels” are really intended to be historical biographies. So we must treat them in that manner. They were histories before they were the four Gospels of the NT, not the other way around. Given that they are intended to be histories, what does this mean? It means that this man, Jesus, had four biographies written about Him within 60 years of His life (I would say death but obviously that would stir up a controversy). Now that’s what I call impressive! Julius Caesar had only one secular historian mention him till nearly 150 years after his life. The five main histories we have about Alexander the Great weren’t authored until 400 years after his life. And last time I checked, nobody wonders why Julius Caesar only had a few people that had a vested interest in him wrote about him.
Enough background info. The only times Jesus is mentioned outside of the Gospels is about stuff that concerned the parties writing. Like the fact that he “suffered the extreme penalty under the reign of Tiberius..”(Tacitus). So while the answer seems so simple, it really is. Jesus had more histories written within a shorter period of time than most figures of antiquity. And these sources happened to be canonized into the Bible and are now often considered unhistorical because of this.