He said he was (punishable by death, which is what happened), he acted like he was (miracles, etc.), and taught things that were completely contradictory to the times they lived in. You might even call them modern (gender equality, etc.). They definitely weren't like political ideas that change gradually over time. People who knew him believed it enough to die (not for political power like early Muslim martyrs). Jesus was either who he said he was, or a complete lunatic, or one of the most evil liars of all time. What did he have to gain by claiming he was God, but refusing to lead a rebellion against the occupying Romans? That was a popular notion among Palestinian Jews of the time, and would have gained him significant political power.