666 is the number of the Beast, the Antichrist.
Revelation chapter 13 verse 18 – This calls for wisdom. If anyone has insight, let him calculate the number of the beast, for it is man’s number. His number is 666, six hundred, threescore and six.
In the Bible the number 6 represents man (unholy), whereas the number 7 represents Christ (holy) and the number 3 denotes the holy Trinity (Father, Son, Holy Ghost).
666 means ‘unholy trinity’, (Satan, the False Prophet, the Beast).
The ‘mark’ of the Beast is widely debated amongst religious scholars today. However, the ‘number’ of the Beast is unanimously perceived as being 666.