The following comes from "The Interpreter's Dictionary of the Bible", Vol 4, pages 594-595, edited by G.A. Buttrick. This is a respected publication and is relied on 32 times in the WTS's 2 volumes: "Insight on the Scriptures". The following excerpt from "The Interpreter's Dictionary" is speaking of the earliest times of Christianity:
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The NT is now known, in whole or in part, in nearly five thousand Greek MSS alone. Every one of these handwritten copies differs from every other one. In addition to these Greek MSS, the NT has been preserved in more than ten thousand MSS of the early versions and in thousands of quotations of the Church Fathers. These MSS of the versions and quotations of the Church Fathers differ from one another just as widely as do the Greek MSS. Only a fraction of this great mass of material has been fully collated and carefully studied. Until this task is completed, the uncertainty regarding the text of the NT will remain.
It has been estimated that these MSS and quotations differ among themselves between 150,000 and 250,000 times. The actual figure is, perhaps, much higher. A study of 150 Greek MSS of the Gospel of Luke has revealed more than 30,000 different readings. It is true, of course, that the addition of the readings from another 150 MSS of Luke would not add another 30,000 readings to the list. But each MS studied does add substantially to the list of variants. It is safe to say that there is not one sentence in the NT in which the MS tradition is wholly uniform.
Many thousands of these different readings are variants in orthography or grammar or style and have no effect upon the meaning of the text. But there are many thousands which have a definite effect upon the meaning of the text. It is true that not one of these variant readings affects the substance of Christian dogma. It is equally true that many of them do have theological significance and were introduced into the text intentionally. …
It has been said that the great majority of the variant readings in the text of the NT arose before the books of the NT were canonized and that after those books were canonized, they were very carefully copied because they were scripture. This, however, is far from being the case.
It is true, of course, that many variants arose in the very earliest period. There is no reason to suppose, e.g., that the first person who ever made a copy of the autograph of the Gospel of Luke did not change his copy to conform to the particular tradition with which he was familiar. But he was under no compulsion to do so. Once the Gospel of Luke had become scripture, however, the picture was changed completely. Then the copyist was under compulsion to change his copy, to correct it. Because it was scripture, it had to be right.
Many thousands of the variants which are found in the MSS of the NT were put there deliberately.
They are not merely the result of error or of careless handling of the text. Many were created for theological or dogmatic reasons (even though they may not affect the substance of Christian dogma). It is because the books of the NT are religious books, sacred books, canonical books, that they were changed to conform to what the copyist believed to be the true reading. His interest was not in the "original reading" but in the "true reading." This is precisely the attitude toward the NT which prevailed from the earliest times to the Renaissance, the Reformation, and the invention of printing.