Dan B. Wallace on the Nature of Textual Variants.

Textual Variant: Any place among the manuscripts in which there is variation in wording, including word order, omission or addition of words, even spelling differences.

The most trivial changes count and even when all the manuscripts except one say the thing then that lone manuscript reading counts as a textual variant. 

There are about 300000 to 400000 textual variants.

There are only about 140000 words in the new testament.

The reason we have a lot of textual variants is that we have a lot of manuscripts.

This was discovered by Richard Bentley is a Brilliant textual Scholar 300 years ago in his works "Remarks upon a discourse of free thinking"

Richard Bentley commented on the work of John Mill of 1701 (who found 30000 variants from about a 100 manuscript quoted by Bart Ehrman)

Richard Bentley: commented in 1713.

"If there had been but one manuscript of the Greek Testament at the restoration of learning about two centuries ago, then we (would have) had no various readings at all... And would the text be in a better condition then, than now [that] we have 30000 [variant readings]? It is good, therefore... to have more anchors than one; and another manuscript to join the first would give more authority, as well as security."

Today in Greek alone we have

Greek manuscript: 5600+

Many of these are fragmentories specially the older ones.

But the average Greek new testament manuscript is over 450 pages long altogether there are more than 2 and a half million pages of text leaving 100s of witnesses for every book of the new testament.

Total number of manuscripts 20000.

Destroy all these and we still have 1 million quotations of the new testament from early church fathers. 

Bruce Metzger & Bart Ehrman:

"If all other sources for our knowledge of the text of the new testament were destroyed, [the patristic quotations] going back to the second century and in some cases even the first would be sufficient alone for the reconstruction of practically the entire New Testament."

We have a dozen manuscript from the second century all fragmentary.

64 from the third century

48 from the fourth century

Total 124 manuscripts within 300 years from the composition of the new testament.

Most of these are fragmentories but collectively though the whole new testament has been found in these manuscripts and several books are found in there multiple times.

Only a third of Tacitus' writings are with us.

First copy doesn't appear until

Greco-Roman Biographers and Historians

Pliny the Elder: 200 copies: 700 years

Plutarch: 800 years 

Josephus: 800 years (more than 20 copies none earlier than the 9th Century CE)

Polybius: 1200 years

Pausanias: 1400 years

Herodotus: 1500 years

Xenophon: 1800 years

Revelation 13:18 666

701 years ago a scholar deciphered in an earlier manuscript the number to be 616.

And just 15 years ago another manuscript with 616 was discovered. 

What theological beliefs depend on textually suspect passages?

"It would be a mistake to think that the uncontrolled copying practices that led to the formation of the western textual tradition were followed everywhere that texts were reproduced in the Roman Empire. In particular, there is solid evidence that in at least one major city of early Christendom, the city of Alexandria, there was conscious and conscientious control excercised in the copying of the books of the new testament. Textual witnesses connected to Alexandria attest a high quality of textual transmission from the earliest times. It was there that a very ancient line of text was copied and preserved..." 

Source: Excerpts from a debate between Dan Wallace and Bart Ehrman.

https://youtu.be/wyABBZe5o68