Why do priests wear a chasuble at Mass?

From an article on Aleteia.org:

When attending Mass, you’ll always see the priest wearing a distinctive garment unlike anything in modern-day fashion. It typically has some sort of embellishment or symbol on it, and comes in several different colors.

What is it and why do priests still wear them?

 Since ancient times, whenever a priest celebrated the sacrifice of the Mass he would put on a large poncho-like garment called a casula (chasuble) that covered his ordinary clothing. This vestment developed from the ordinary Roman attire of a farmer, who wore the large poncho to protect him from the elements. It eventually became associated with Christians in the 3rd century.

As the fashion trends shifted the chasuble ceased to be an ordinary garment but was still used by priests. By the 8th century the chasuble was reserved for clergy members and began to be ornamented in a way that reflected its sacred function.