What is the expressive function of "rolling" in "Xiao drives a charcoal chariot over an ice track"?

Describing the cold weather and the heavy things on the car, it paved the way for the following "half a piece of red yarn and one foot of silk, tied to the cow's head and filled with charcoal".

It freezes because of the cold, and the cargo is heavy, so it leaves traces on the hard ice. In such weather, the charcoal seller who had to go out to make a living ended up with only a piece of worthless fabric. This is far from the value of a load of charcoal, but he has no ability to resist, because this is the official taking people's wealth at a low price.

Here it reveals the reality that the common people are subjected to wanton exploitation by the exploiting classes, reveals the darkness of the society at that time, and at the same time shows the author's deep sympathy for the working people at the lower class. Extended information

In order to satisfy their decadent and luxurious life desires, the feudal ruling class, in addition to imposing numerous exorbitant taxes and miscellaneous taxes, also adopted other means to rob the people of their blood and sweat. After the mid-Tang Dynasty, the imperial court often sent people to the market to purchase items. As soon as they saw something they liked, they would pay them a very low price or plunder it at will. Sometimes they would ask the owner to bring the goods into the palace, then rake them up and extort "door money" and "feet" from the owner. Price".

Bai Juyi witnessed this kind of bad government with his own eyes when he was in Chang'an, and he felt very angry. Although he failed to show the rebellious spirit of the working people in "The Charcoal Seller", he dared to boldly expose the evils of the "palace market" and showed the greedy and tyrannical face of the rulers with the emperor as the main backing, using his unique poems The form reflects it, which is indeed commendable.

In this small narrative poem, the author uses line drawing to successfully create a touching image of the old charcoal seller. The article reflects the very miserable life situation of the old man. At the same time, it is written in this way to make the following paragraph "a cart of charcoal weighs more than a thousand catties, and the palace envoy will not be able to bear it", which appears more powerful and can arouse readers to the "yellow messenger" who pretends to be a tiger. The hatred of "Bai Shier".