The reader of the gospel is now required to attend to the themes of a 'Johannine discourse'. If he is to understand the discourses, of which this is the first, he must understand them in their scriptural, biblical setting. Unless he is to do grave violence to the text, he is not free to put them in any other setting, ancient or modern. The Fourth Gospel is a biblical book, and the first discourse is spoken to a Jewish Rabbi. If these discourses seem to us to be so full of gaps that they appear to leap rather than move; or if, alternately, they seem to us to be monotonous; or if they seem to be set quite out of their context by the introduction of the Evangelist's own comments; we must not be satisfied with these judgments of ours, since the Evangelist most assuredly did not think that what he wrote was fragmentary or monotonous or inconsistent. We must not rest from exegesis until the apparent gaps have been filled up so completely that each discourse moves step by step as an ordered, a theologically ordered, whole: until, that is to say, what is said becomes intelligible and coherent speech, and until, moreover, it coheres with the biblical Palestinian background upon which the Evangelist has set it, even though he be writing in Greek, years after the temple was destroyed and when the Jews no longer congregated in Jerusalem. This is the energy of understanding which the Evangelist demanded of his original readers; and his book still makes the same demand upon us. Also, we shall be unlikely to persevere with such exegesis unless we assume that something important is being said. And above all, we must not rise from the first discourse with the feeling that though Nicodemus is a sensible person, the Evangelist is not.
from page 201, The Fourth Gospel