Jesus was written about by secular historians of the time such as Josephus. Archaeology has proven the existence of many articles spoken of in the Bible.
The Bible has been written by many authors over thousands of years and the main theme of the Bible is the same. Man has sinned against God and God made a Way for man to be perfect, without sin, before Him.
Hundreds of prophecies were written about the Savior or Messiah who would take away the sins of the world. Jesus Christ fulfilled every prophecy with His birth, life, death, and resurrection.
It is basically impossible for Jesus not be who He said he was. He is the I Am.