The verb prove … guilty is translated “convict” by most translators. When used with a personal object, the verb basically means “to show (somebody) up for what he is.” Here the personal object is “me,” which is followed by the phrase “concerning sin,” and so the entire expression means “to show that I am guilty of sin.” This meaning is also conveyed by such a translation as “convict me of sin,” but this expression may prove ambiguous to the average reader. New English Bible reads “convicts me of sin” in its footnote, but in the text it has “can prove me in the wrong.” The question is whether Jesus is claiming to be sinless in an absolute sense, or that he is right in what he is saying in this particular controversy. Although either viewpoint is justified by the context, John could have expressed himself more clearly and unambiguously if he had intended the second meaning. The word sin seems to be used here as it is used elsewhere in John’s Gospel, and not merely in the sense of “to be in the wrong.” This opinion is evidently held by most commentators and translators.

Believe me has the same force here as in the previous verse.

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 .