I am not sure how to crosspost here from stackexchange.
Can someone please help this poor bloke?:
https://physics.stackexchange.com/questions/767222/what-is-the-physical-meaning-of-the-vacuum-state-in-the-bcs-ground-state#comment1721506_767222
I took a course on Condesed Matter Physics 1 that covered a little bit of Tinkham's book not all of it, so I cannot help more than I have suggested there.
CHEERS!