on Just Publishing Advice:
Should you add a comma before and in a list of three or more items? Yes, because it eliminates confusion in a sentence.
The comma before the word and in a list of three or more things is the Oxford comma. It’s also called the Serial comma.
Writers use it to separate the last item in a list to avoid uncertainty or misunderstandings.
One classic example that is often quoted is, to my parents, Ayn Rand, and God. Without the comma, it could be misconstrued that the parents were god and Ayn Rand.