The answer would be:
to inform the audience of the events leading up to this point
In Hamlet Horatio is a logical thinker and trusted by the people by making him giving this speech he tells the story to the people and people belive him, this way hamlet uses the trust people have in horatio so unveliebable events such as ghosts of dead kings talking to their children wont sound so crazy.
The answer is: inaction.
Quietism was a movement which started in Spain, France and Italy in 1600s. It believed in the passivity of spirituality and in a contemplative life. It also assumed that perfection could be achieved by the abolition of will, so God would approach someone when its soul is in a quiet state, without any reasoning or executing any actions. As a result, man would accept whatever God grants him.