Rolling

Here is a qstn I saw another forum :

For many, a major portion of Chi Sao is the “rotation, or rolling”. My question to you is why Roll? What is the purpose of the roll? What is the cause and effect?

I would like to see what everyones response is to this qstn.

Ask your instructor. He shows you what forward pressure is al about. Can´t easily explain feeling in just a few words.

IMO the purpose of the roll is change, and the cause and effect are intent.