Describe Virgil's function in the Inferno. How does he differ from Dante?

In The Divine Comedy, Virgil acts as Dante's guide and mentor. His unfailing wisdom and patience help Dante get through the many trials and tribulations he endures on his epic journey, stiffening his resolve in the face of all manner of adversity. The ancient Roman poet was deeply venerated by learned medieval Christians like Dante, who regarded Virgil as a virtuous pagan. This was mainly because of the Fourth Eclogue, which Christians interpreted as prefiguring the birth of Christ.
However, Virgil was still a pagan for all that, so although he can lead Dante to the gates of Paradise, he can go no further. This is an allegory on the place of pagan learning in Renaissance Europe. Renaissance thinkers drew deeply upon the wisdom of the ancients but believed that having faith was necessary to achieve beatitude. As a pagan, Virgil is unable to provide any guidance in this respect, so he must be absent during the final stages of Dante's epic spiritual journey.