I am reading through BCS's original paper from 1957 on PhysReview. It is very difficult for me to actually understand every word it says, I am unfamiliar with most terminology the paper mentioned. However I know most of the very basic mechanism of this theory. I understand how superconductivity came to form but I just still find it unclear with the Meissner's effect. I am not sure if I have misread it or it just does not explain Meissner's effect explicitly. I think what B. C. S. are arguing is that Meissner's effect is a consequence of energy gap, and from my understanding energy gap is the energy required to break Cooper's pairs. So why is Meissner's effect a consequence of energy gap? or somehow related to it? Does it give lower energy to the system when magnetic field isn't penetrated through the system? Thank you for your time.