© 2003 by T.L. Hubeart Jr.
Mark 1:2 (KJV) As it is written in the prophets, Behold, I send my messenger before thy face, which shall prepare thy way before thee.
Modern texts and translations (and even a venerable, generally Textus Receptus-based version like the Spanish Reina-Valera Bible of 1909!) give "as it is written in Isaiah the prophet" (ASV). Scholars assure us that the modern texts give the original reading here, and that scribes changed an original reading of "in Isaiah the prophet" to "in the prophets" (as in KJV).
Allegedly this was done in order "to rescue Mark from a (misapprehended) error in citing Isaiah when the quotation is from Malachi and Isaiah together," as James White claims (The King James Only Controversy, p. 254). (The quotation starts with Mal. 3:1 before continuing with Isa. 40:3.) White attempts to back up this assertion by paralleling this verse with Matt. 27:9, where scribes did the same thing in certain MSS. for a similar reason, changing "Jeremiah" to "Zechariah." In Mark 1:2 "it is much easier to understand why a scribe would try to 'help Mark out,'" this author insists (ibid., p. 168), than to know why "in Isaiah the prophet" would replace "in the prophets."
But it seems to me that the problem could also be viewed convincingly from the opposite position. Imagine a scribe copying the opening of Mark and recognizing the familiar Isaiah passage cited in 1:3. It is fully as credible to have him "helping Mark out" by providing the reference--perhaps in the text itself, perhaps in a marginal note that was later miscopied into the next generation of MSS.--as it is to postulate that the reverse occurred. In fact, Wilbur Pickering (in The Identity of the New Testament Text, rev. ed., pp. 89-90) considers it clear that "assimilation" has here been done by copyists, seeing that "The only other places that Isaiah 40:3 is quoted in the New Testament are Matt. 3:3, Luke 3:4, and John 1:23," which "all identify the quote as being from Isaiah (without MSS variation)." So a copyist might have considered himself to have been improving the general reference by changing it to the specific one found in the other gospels--without apparent regard for Mark's use of Malachi preceding the Isaiah quote.
Indeed, to reverse the question, one might ask why, if there were an original reading of "in Isaiah the prophet," a scribe helping Mark out would on his own initiative have written "in the prophets" rather than the more immediately accurate "in Malachi the prophet"--assuming he knew his major and minor prophets well enough to feel the need for correction in the first place!
By the way, we need not remain entirely in the realm of speculation on such a question, but can examine an analogous case which I think undercuts some of White's assumptions cited above. There happens to be a clear instance of just what I have described--a scribe "helping out" the text of one of the gospel writers by inserting a prophet's name--in Matt. 13:35, as pointed out by Burgon (Last Twelve Verses of S. Mark, p. 81). In that verse, a scribe amended "spoken by the prophet" to insert the name "Isaiah" (so in Codex Aleph [original hand], Codex Theta, Family 1 and 13 mss. and a few others, according to Nestle-Aland 26). And as is the case with Mark 1:2, the specific identification is quite mistaken, since the verse in Matthew reflects a quotation from Ps. 78:2, not from Isaiah.
Further, the manuscript evidence for the KJV's reading at Mark 1:2 is by no means negligible; according to UBS-4, it appears in Codex A ("Alexandrinus") and Codex W, both from the fifth century, as well as the majority of Byzantine mss., the Latin version of Irenaeus' writings (see his Against Heresies, Book 3, ch. 10, para. 5), the Harclean Syriac, the writings of Asterius (4th century), and many others.
Accept the KJV with full confidence, since the moderns here, as so often elsewhere, have not proven their case.