The way the Main Quest is supposed to run, you get a few messages that you need to go talk to the Archcanon in Vivec as soon as you finish the Third Trial.
Under normal circumstances, you are told to come back to see the Archcanon when you have been named Nerevarine of all four Ashlander Tribes and Hortator of all three Great Houses. This is supposed to let you know where to go after you have taken care of the Fourth and Fifth Trials. The door to the Archcanon's office is locked and guarded and you will not get the key until you have finished the Fourth and Fifth Trials.
However, if you are the Archcanon, the door is not locked (you had to open it in order to get to the Archcanon's quests) and the Archcanon will talk to you. His message: Vivec would like to talk to you, so here's the key to his palace.
Vivec presents you with Wraithguard and tells you what you need to do to defeat Dagoth Ur (as well as answering a lot of questions if you keep asking about "business"). He also rescinds his edict on the persecution of the Dissident Priests and proclaims you Nerevar reborn.
In effect, by following up on the game's hint, you completely circumvent the Fourth and Fifth Trials. Since a lot of events in the game depend on which entries appear in your Journal, it would be well to simply take Wraithguard and then go on to get the Tribes and Houses behind you.
If you do not want any nasty surprises, though, simply pass on the visit with the Archcanon until you have completed the Fourth and Fifth Trials.