Now is the emphatic position in the Greek sentence structure.

You know everything must be taken as a reference to verse 19, where Jesus answered the disciples’ question before they asked it, indicating that he knew what was in peoples’ minds (see 2.24-25). It is in this light also that their statement you do not need someone to ask you questions must be understood. The verb rendered ask … questions (so also New American Bible) is erōtaō (see verses 23 and 26), and relates to requests for information. On the basis of the observation that Jesus knows what is in their minds, and is able to answer their questions even before they ask him, the disciples respond by saying This makes us believe that you came from God. This makes us believe (so also Moffatt, Goodspeed) is literally “by this we believe” (Revised Standard Version), and is rendered “because of this we believe” in Jerusalem Bible and New English Bible.

In some languages it may be necessary to distinguish between two meanings of the verb know. In one meaning We know may be equivalent to “we are certain” or “we are sure.” The other meaning of know indicates complete comprehension. Hence, the first clause in verse 30 may be translated “we are certain that you comprehend everything.”

You do not need to have someone ask you questions is a semantically condensed expression. It really means that “in order to know what questions people have in their minds, it is not necessary for you to ask them what they are thinking.” It may be necessary to employ such a rendering to express the meaning of the second clause of verse 30.

This makes us believe involves a complex causative relation in some languages. This relation may be expressed as “because of this we believe” or “because you know what people are thinking, we believe.”

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 .