And so is explained by because Isaiah also said, but the Good News Translation restructuring of this sentence does not make the connection clear. Compare, for example, New American Bible, “The reason they could not believe was that, as Isaiah says elsewhere….” And so could, of course, be interpreted as result, for example, “And as a result they were not able to believe.” Such an expression approximates closely the idea of cause, but it may be better to make the cause more specific, for example, “The reason why they could not believe was that…” or “The reason they could not believe was because, as Isaiah had also said, ‘God has blinded their eyes….’ ”

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 .