author of John obviously believed in the doctrine of either divine subordinationism of the son , or docrtrine of equal trinitism of the son. As can be seen in first verse John 1:1 as written by the author. So if the author believed in the son being equal in authority to Yhwh, thus it is no issue for the author to say Jesus will be the one to send the advocate , and not Yhwh. As both have equal authority (from the point of view of author).
there are many translation for Isaiah 29:12
And the book is delivered to him that is not learned, saying, Read this, I pray thee: and he saith, I am not learned.
verse 29:10-12 talks about vision even the most learned people will not be able to read the book, and the unlearned will obviously not able to read it.
this particular book will be able to be understood in later times, and the Israelites shall rejoice upon the time when it reaches them.
Problem with Israelite, is that will they accept the decree of God of Israel in the book