What reason does marcellus give for inviting horacio to observe the watch ?

The answer is quite simple, to “approve and avouch for the coming of the apparition with the gross and scope of his intellectual opinions”.

Indeed, Horatio is a scholar from the University of Wittenberg. The guards are uncultured and possibly illiterate they do not trust their judgment and defer to Horatio to ascertain the exact nature of the ghost.

In the Middle Ages, ghosts were regarded with suspicion. It was considered that they might be either a ruse from pranksters, a demon in disguise, a hallucination and if all of the former had been disproved, the actual wandering, tormented soul of a deceased human being.

yeah, i think its a good thing what do you think?

the purpose of the heading in the passage is to identify who is telling the story.

this excerpt is part of the book sugar changed the world (2010) written by marc aronson and marina budhos. as the book has been written by two people, the heading "marc" indicates that this specific excerpt is being narrated by aronson. in the fragment, marc describes his grandfather's story after hearing it from his cousin. however, there are other excerpts where budhos is the one that tells the story of her family.

aronson and budhos, who are husband and wife in real life, decided to write sugar changed the world when they found out how sugar, which had an important role in slavery and economy, changed their ancestors' lives.