He causes all, both small and great, rich and poor, free and slave, to receive a mark on their right hand or on their foreheads, and that no one may buy or sell except one who has the mark or the name of the beast, or the number of his name. Here is wisdom. Let him who has understanding calculate the number of the beast, for it is the number of a man: His number is 666.  (Rev 13:16-14:1 NKJ)

Governments throughout the centuries have used various code systems to send and receive classified, secret messages that they didn’t want to fall into the hands of the enemy. Today encryption is used whereby only those with the code can read certain messages. 

John is writing to seven first-century churches in what is modern day Turkey. The ruling government is oppressive and anti-Christian, and the antics of Emporer Nero make ISIS seem like pussycats.  The modern day Basilicas of St. Peter is built on the site of Nero’s Circus where the citizens of Rom would come to be entertained. There you would find chariot races, Gladiator fights, and the killing of Christians by throwing in with wild animals or dipping them in oil, tying them to a stake and setting them on fire. His hatred for Christians increases after the great fire of Rome in AD 64. Nero was regarded as a beast and when he finally committed suicide, somewhere happy, some sad and a large majority scared that he would come back.  So strong was this belief that even Augustine of Hippo wrote about it in AD 422. Three imposters, claiming to be a reincarnation of Nero, tried to lead rebellions.

The beast with seven heads and the number 666 seem to allude directly to emperor Nero (reigned AD 54-68). Though John didn’t write Revelation in the 60’s, the impression Nero made and the story of his return made a huge impression.  The Emperor of the day, Domitian, was also a persecutor of the church.  

But what about all this so called Bible prophecy? The Revelation of Jesus Christ was never intended to be a  prophetic book, and though it does contain some Messianic hope for the future, John merely wanted to encourage the Christians of his day.  In short, the dispensational teaching of Revelations is a pack of lies.

Going Deeper…

In both ancient Greek and Hebrew, letters also represented numerals (as they do in Latin), their values assigned according to the order of the alphabet, alpha, and aelph, for example, having the numerical value of 1. By adding these values, words could be represented as the sum of their numbers. This literation of numbers and numeration of letters was known as isopsephism by the Greeks and gematria by the Jews (which, in cabalistic practice, has been used to interpret Hebrew scripture). If the Greek letters of Nero Caesar (Neron Kaisar) are transliterated into Hebrew (nrwn qsr), the numerical of these Hebrew letters equals 666. One should appreciate, by the way, that there were no numbers in Greek or Hebrew and that the “the number of the beast” was not presented as a figure but as letters of the alphabet or written in full. That is to say; it was not expressed as “666” (indeed, discrete Arabic numerals would not be invented for another five hundred years) but as the numerical values of the three letters representing 600, 60, and 6.

http://penelope.uchicago.edu/~grout/encyclopaedia_romana/gladiators/nero.html