It is important to realise the way in which the function of Virgil as a character operates symbolically as well as literally. Many critics argue that Virgil is somebody who represents human reason, which has the capacity to care for and guide the individual as they venture through the sinful world where we are placed. If we consider Virgil's traits in this text, we can see how they support this interpretation: he is wise, sober, determined and practical. At various points in the text he protects Dante from various monsters and forces of evil.
He is also used to comment on the various stages of hell that Dante visits. Note hte way that in Canto VIII he is shown to be powerless outside the gates of the city of Dis. This is both used to foreshadow the greater terrors of Lower Hell as well as emphasising the way that reason is helpless without faith, as Virgil's dependence on the angelic messenger indicates.
Virgil therefore acts as Dante's mentor/protector/guide in this text, not only literally guiding him through his tour of hell but also stopping to highlight the moral lessons of the text that Dante is trying to convey. Virgil often shows that he becomes impatient with Dante when he is slow to pick up these lessons. Today's audience would pick up on the image of Virgil as a mentor and a guide.