Final answer:
Marcellus says that Horatio confirmed the Ghost resembled the late King Hamlet. Horatio's presence at the night shift was crucial because his scholarship might help communicate with, or understand, the apparition, thus advancing the play's plot.
Step-by-step explanation:
In Shakespeare's play, Hamlet, Marcellus repeats Horatio's declaration that the Ghost resembles the late King Hamlet - meaning that it is an apparition or spirit of the dead king. When Marcellus and Bernardo first see the Ghost, they are horrified and invite Horatio to their night shift because he is a scholar.
They believe Horatio is more likely to communicate with the Ghost and convince it to explain its appearances. Horatio's presence instills a level of trust and intellectual understanding regarding the supernatural events the guards are witnessing, making it an essential element in the advancement of the plot.
Learn more about Hamlet's Ghost