The reason Christians/Jews think the barcode is the mark of the beast is because the three bars, on the left, middle, and right that dont have numbers under them are actually 6’s. That’s 666. “The mark of the Beast” “Man’s number” as said in the book of Revelations. It even says people wont be able to buy or sell without that mark.
(http://www.youtube.com/watch?v=iC70PtB6zyc)