Take a look at this picture. Do you know why it is so important?
If you're an art student, you would probably answer with something like this:
One of the most admired frescos from the Arena Chapel done by Giotto, known as the "Father of Picturial Painting". It shows real emotion and human suffering. Uses focal points instead of symmetry, overlapping figures and shading. Done in Italo-Byzantine style, it breaks from the stylistic other-worldness of the Byzantine style of the Dark Ages, with its introduction of naturalism.
However, if you take into the account of the cultural and religious significance of this piece, it becomes so much more than the epitome of a style of painting.
To appreciate Giotto's work, you need to understand that in the Dark Ages, artists painted figures to look other-worldly to reflect the supernatural and unfathomableness of Christ and the saints. These were not persons who could be related to in a normal fashion. These were impersonal beings, who only interacted with we unworthy and insignificant humans out of supernatural mercy.
To this end, the populace were treated to paintings like the one to the left here. Faces that showed no emotions. Images that showed not connection to the things of this world. During the Dark Ages, God was not Love, but Power.
Look again at the Byzantine representation of Christ. Is the image a welcoming one? Does this look like someone who emanates love? Someone who had a personal interest in your salvation?
It doesn't to me.
On the other hand, look again at Giotto's Christ. Is there any doubt that the man lying there had a connection to those around him on a personal level? That they felt his love for them in their life?
To the best of my knowledge, Giotto was the first person to paint Christ in a personal way. Perhaps herding sheep as a child made Giotto feel a special kinship with Jesus Christ. Perhaps being chosen by the master painter Cimabue as a humble lad from the country, Giotto saw more of God's love in the world around him, instead of the power plays of rulers and religious leaders.
Whatever the reason, so moving and innovated was Giotto's works, that he was in high demand and other artists began to follow suit. Soon, many who could not read, much less have access to the Holy Scriptures, had a different insight into the nature of Christ - where they actually meant something to the universe and their Creator.
A description of Giotto from http://www.ibiblio.org/wm/paint/auth/giotto/
Giotto was short and homely, and he was a great wit and practical joker. He was married and left six children at his death. Unlike many of his fellow artists, he saved his money and was accounted a rich man. He was on familiar terms with the pope, and King Robert of Naples called him a good friend.
Rereading what I wrote, I realized that I need to explain that the rediscovery of humanism started at the same time that Giotto began his work. And, frankly, I think that his work was a main factor for its re-emergence.