We are blessed with thousands of New Testament manuscripts (over 5,000 fragments) due to the work of many scribes copying the Scriptures throughout the centuries.  This blessing also poses a challenge because many of these writers made changes to the Biblical texts.  The variances or errors introduced deviate from the autographs, and generally only cause minor changes to the meaning, but can be unwound by scholars to reveal with a high probability what the original texts said.

Consider a situation where you receive an important handwritten letter (considered the original autograph) and want many others to be able to read it.  Before the printing press, you’d have had to copy it manually (creating a first generation copy) and maybe have your friends copy it as well to speed the distribution.  As the letter was rewritten, one person may misread a word and write it down incorrectly, another might try to help out by attempting to fix what she thought was an error in the letter and another friend might forget a word because of being interrupted while writing.  Over time, other people my decide to rewrite the letter as well (creating a second generation) and introduce further errors because of misreading handwriting or due to an attempt to clarify a word so that their readers would better understand the letter based on their customs.  Transmitting the letter in this way could go on for many, many generations and introduce hundreds of variances in the letter based on who scribed it and the source document the scribe worked from.  As a result, there become many similar, yet not exact versions of the original letter with much of the meaning continuing, but containing differences in some words or sentences from one version to another.

The science (and art) of unwinding the differences and tracing them back to the original text is called textual criticism.  Textual criticism is helpful to understand variances, but is controversial  as well because many of its practitioners remove large sections of Scripture.  Bruce Metzger was one of the leading (conservative) scholars of New Testament texts and created a list of the types of error that crept into the Scripture that is helpful in understanding how and why the changes introduced over time:

• Unintentional changes
  • Errors from faulty eye sight – confusion of similar letters (think c and o or m and n in English) resulting in different words or skipping lines that look similar in the text
  • Errors from faulty hearing – the text was sometimes read so it could be copied by multiple scribes; if two different words were pronounced the same they could be mixed up (think red and read or there and their)
  • Errors of the mind
    • Substitution of synonyms
    • Variations in the sequence in words
    • Transposition of letters within a word
    • Usage of the wording of one passage based on a similar passage (think of the synoptic Gospels that tell similar stories slightly differently)
  • Errors of judgment – explanatory notes in the margins of texts incorporated into the text itself
• Intentional changes – this includes correcting what was thought to be an error or attempting to alter the text to make a doctrine more clear or explicit
  • Changes involving spelling or grammar
  • Harmonistic corruptions – intentionally ‘fixing’ the text to make it align with a similar passage (e.g., Lord’s prayer) or Old Testament reference (to make it better conform to the original text)
  • Addition of natural complements and similar adjuncts – examples would include adding “and Pharisees” to a passage the referenced scribes only or ‘enhancing’ Jesus by including “Lord” before His name when only only his name was mentioned in the text
  • Clearing up historical and geographic difficulties – editing what were thought to be mistakes such as how a place was described or which prophet a quotation was attributed to (Zechariah rather than Isaiah)
  • Conflation of readings – merging of two variant readings together when there were differences in manuscripts such as when one manuscript referenced “God” and another referenced “Lord” in the same passage the words were merged to read “Lord and God” rather than selecting one or the other
  • Alterations made because of doctrinal considerations – removal of problematic passages or changes to phrases to support a desired doctrine
  • Addition of miscellaneous details – examples include naming the criminals crucified with Jesus, adding to Jesus genealogy and providing apocryphal details about Jesus baptism

Source: The Text of the New Testament – Chapter 7