What has the Holy Spirit taught people after Jesus left? I know that the below verse is explained to foretell the coming of the Holy Spirit according to Catholics.  Even though the Holy Spirit was already mentioned previously, it is explained that Jesus is saying when he comes he will guide you into all the truth.


  12 “I have much more to say to you, more than you can now bear.  13
  But when he, the Spirit of truth, comes, he will guide you into all
  the truth. He will not speak on his own; he will speak only what he
  hears, and he will tell you what is yet to come.


I want someone to explain to me the following:


What exactly has the Holy Spirit guided people to in terms of 'All Truth'.
Why was this truth something the people at Jesus's time could not bear?
If it is the Holy Spirit, and if the HS is the 3rd person of the Trinity, why can He not speak on His own?


Note:  I'm looking for an answer that fulfills the criteria of the verse 1) cannot bear it now 2) guiding to all truth  3) tell you what is yet to come  etc.

In addition, if the Holy Spirit is considered God, why would not speak of his own, but only what he hears?  If he is God, he will have authority on his own.

I am asking because I believe it was Tertullian, the famous Church Father, who ended up being declared a heretic because he believed this was referring to a person (it sure sounds like it to me also - the holy ghost was already mentioned to be present anyhow).
Cardinal Henry Edward Manning, an Anglican who converted to Catholicism, was the author of the First Vatican Council's definition on papal infallibility in Pastor Æternus. He wrote an excellent book on the question of the role of the Holy Ghost in the Roman Catholic Church:

The temporal mission of the Holy Ghost : or, Reason and revelation (1865)

Briefly, the Holy Ghost has taught us many things; He has


guarded the deposit of faith or Revelation in all its truth,
prevented the Church from teaching error,
guided the development of doctrine,
given council to the church (and all His other gifts, too),
enabled the Church to interpret the true sense of Scripture,
ensured the infallibility of the Pope when he defines dogma pertaining to faith or morals (e.g., the Marian dogmas of the Immaculate Conception and Assumption),


etc.