In the phrase you will not believe the pronoun you is emphatic, as is the pronoun I in the last sentence of verse 25. A sharp contrast is drawn between the I of verse 25 and the you of verse 26.

You will not believe is more literally “you do not believe” (so most translations); New American Bible has “but you refuse to believe,” and Die Bibel im heutigen Deutsch “you would not believe.” The idea of will may also be involved here, as it is in the first part of verse 25 (you would not believe).

After the clause because you are not my sheep, some ancient manuscripts add “just as I told you.” No modern translations include this clause in their text, and the UBS Committee on the Greek text considers it a scribal addition. It is possible that it was deliberately omitted by some scribes because they could not find in the earlier account any saying of Jesus that these Jews were not his sheep. Absolute certainty cannot be achieved, but it is suggested that the translator follow the decision of the UBS Committee, which also is the conclusion of most modern translators.

At this point John reintroduces the metaphor of the sheep, and it may be necessary to mark this figurative usage as a simile, for example, “because you are not my sheep, so to speak” or “because you are not my sheep, as it were.”

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .