The Basics of Judaism: G-d & Torah: The Text of the Bible:
Has the text of the Bible been preserved exactly?
In many places, the Talmud, the Midrash and the
Rishonim appear to have had different spellings
or punctuations of words in the Tanach than we do.
For a long list see Gilyon Ha-Shas on Shab.55b.
Some of the discrepancies may be due to quoting
verses from memory, but many of them seem to be
due to differences in the masorah (the tradition
about the text). The Bible is of Divine origin,
but since G-d gave it to us, the preservation
of the text has been in human hands. It has been
preserved very accurately, but total perfection
is not possible for humans to achieve.
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