Recent comments on this site encourage me to write a series of blog posts to help nuance such a declaration.
We do not have a single original biblical manuscript. We have copies. And, careful as we know that those who copied have been, the different copies do not all agree with each other. There have been errors and alterations made in the process of copying. This is so for other ancient texts as well, not just the Bible. In the plethora of biblical manuscript copies we have there are many minor and a few somewhat major differences.
The process of trying to establish, as closely as possible, the original text is called “textual criticism”. This is not an exact science. Scholars will disagree.
Some of the tools a textual critic would use include examining in how many manuscripts a particular text occurs, the dates for these manuscripts, where these manuscripts were found, theorising about possibilities that could have caused varying texts, and attempts to explain the origin of other texts.
An example of Textual Criticism
For an angel went down at a certain season into the pool, and troubled the water: whosoever then first after the troubling of the water stepped in was made whole of whatsoever disease he had.
This verse is obviously present in some manuscripts but it is absent from our earliest and best manuscripts and witnesses. This verse is present in some texts where it is marked with asterisks or obeli indicating that it is spurious. This verse includes words not normally used by John elsewhere, including three words found nowhere else in the whole New Testament. Verse 4 actually comes in a wide diversity of forms. It is easier to account for a scribe adding an explanation like this, than why many scribes would remove such an explanation. Most textual critical scholars, hence, would suggest that this verse was not present in the original text of John.
I hope this nuances, for example, someone who stands up and says: “The Bible says in John Chapter 5 verse 4, “For an angel went down at a certain season into the pool, and troubled the water: whosoever then first after the troubling of the water stepped in was made whole of whatsoever disease he had.”…”
This series is to be continued…