There is actually a lot of historical evidence for the existence of a Nazarene leader in the early 1st century. Flavius Josephus’ 1st century chronicle of the history of the Jewish people and Tacitus history of the Roman Empire are both regarded as highly respectable historical texts.

Whether he was the son of god or just a notable leader who said some wise things is largely down to your own opinions but consider that until Constantine adopted Christianity as the roman state religion, early followers of Jesus faced abject persecution by the romans and were willing to die for their beliefs, a belief system that promoted peace and forgiveness.

These weren’t some terrorist group willing to martyr themselves but rather their only crime was refusing to acknowledge the divinity of the emperor. If those early followers didn’t believe Jesus was who he said he was his movement would never have escaped the first century.

And at this point there is no bible and no book. They revered the Jewish texts for their context but their only reference material were hand-copied eyewitness accounts and letters.