Why don't people know what the mark of the beast, if they are Christians?

There is so much to Christianity, and there is no way to know everything about it. Only God can.

Just like not even the cops and maybe not the government or president can know all the laws.

No doctor can know everything about the body as it is too complex, not a specialized doctor, not a general doc, not a dentist, and not a pediatrician. Each body part is too complex to know everything about it.

So just like that, they can't know everything, and maybe not introduced to the mark of the beast.

"666" was used in the book of Revelation as a "code" for the Emperor Nero. Revelation is an Apocalypse, and thus written in symbolic language, to keep the author alive. Those "in the know" understand the references, but, the authorities don't, which kept John from being arrested, and killed.

This also means it should NOT be read literally!

I know what the mark of the beast is, it's something you will have to get either on your hand or forehead or you won't be able to buy or sell.

6 also being the number of a man, antichrist, aka, the Beast. The unholy trinity is made up of Satan, the Beast, and the False Prophet as described in the Book of Revelation.

No one would know or care about mark of the beast if it hadn't been for the movie, The Omen, which made it famous.

6 is also the number for man.

7 is not perfection that is 3, but 7 is the number for completion.

But one has to be careful with all these numbers and not turn them into some type of superstitious divination.

People don't really read their bible as they should so we don't know.

Has this become Yahoo Answer Your Own Question all of a sudden?

On the 6th day of the 6th month of the 6th year of Christ reign, God gave Jesus and the Holy ghost a sword.

666=Nero Caesar in Hebrew numerology. It has nothing to do with being "short of perfection".