This is a sentence from the article "Travel in Southeast Asia". It is about Laos.
In addition to pagodas and historical sites, Wat Sisaket Temple with its big Buddha image, old Hotai library whose walls are covered with sapphires, and wall paintings are well worth seeing.
In this sentence, I am so confused with the following question:
The wall of Hotai library are covered with ____
- sapphires and wall painting
I wanted to know the usage of comma before "and" in this sentence.