In the KJV we have
But he turned, and rebuked them, and said, Ye know not what manner of spirit ye are of. For the Son of man is not come to destroy men's lives, but to save them. And they went to another village.
And in the ESV we have
But He turned and rebuked them. And they went on to another village.
The omission in the ESV (and other versions) of the content of Jesus' rebuke is glaring. Why was it omitted?
It is omitted in versions where the committee of experts behind the translation determined that those words were most likely not in the original text of Luke. In this particular case, the evidence that these words were not original is very strong, though not completely overwhelming.
The shorter version is found in:
Although later documents are more split, such complete agreement among all our early texts is very strong evidence.
Codex Bezae (around 400) has a unique reading with half of the longer version. Codex Bezae has a lot of unusual readings, and is usually considered somewhat unreliable. There are some early Latin and Syriac documents with the longer reading. In fact, the vast majority of Latin manuscripts have the longer reading, which explains how it got into say the KJV.
I've taken this information from here, since it is available free online. A more reliable source would be Nestle-Aland.
Finally, a good place to get quick summaries of issues like this one is the NET bible footnotes. Here the relevant footnote (justifying the shorter choice) reads:
Many mss ([D] K Γ Θ Ë1,13 [579] 700 2542 pm it) have at the end of the verse (with slight variations) “and he said, ‘You do not know what sort of spirit you are of, for the Son of Man did not come to destroy people’s lives, but to save [them].’” This variant is clearly secondary, as it gives some content to the rebuke. Further, it is difficult to explain how such rich material would have been omitted by the rest of the witnesses, including the earliest and best mss.
To assume that it is omitted from the ESV is an invalid assumption. Another possibility is that it was added to the KJV.
There are two different manuscript families represented by the KJV and ESV, so, in reality, the KJV added nothing nor did the ESV omit anything. They simply represent accurately the manuscripts which they translate.
The question then arises as to which manuscript is correct. There is much debate about this, and sometimes it gets incredibly heated. I have read a good bit on this, and it seems to be that the small number of variances in the texts can largely be ascribed to either editorial notes that were added in to the manuscript used for the KJV or phrases copied from one gospel account into another that did not originally contain them. To see a list of these, check out List of Bible verses not included in modern translations.
In this specific case, there is just a variance in the manuscripts. Bible Gateway's listing of this verse includes the following comment on it:
Luke 9:55 Some manuscripts add and he said, "You do not know what manner of spirit you are of; for the Son of Man came not to destroy people's lives but to save them"
It should be stated, though, that no variance in any manuscripts calls into question any doctrine of Christianity in the least bit.
This question goes back to where we get out current Bible from. There are several ancient manuscripts, and there are some minor discrepancies between them.
These words are omitted in the Codex Vaticanus and others.
Luke 9:55–56 – και ειπεν, Ουκ οιδατε ποιου πνευματος εστε υμεις; ο γαρ υιος του ανθρωπου ουκ ηλθεν ψυχας ανθρωπων απολεσαι αλλα σωσαι (and He said: "You do not know what manner of spirit you are of; for the Son of man came not to destroy men's lives but to save them) — omitted as in codices Sinaiticus, C, L, Θ, Ξ, 33, 700, 892, 1241, Old Syriac version (syr), copbo;[31]
For an explanation that goes into more detail about how the current Bible was compiled, ad how these minor issues address whether or not we can trust our current Bible see What is “Manuscript Evidence” and how is it useful?
