I am confused with usage of but when a negative is preceding it. For example
The importance of this bill is not in its specific provisions, but in its broader impact.
Here is the word but doing a contrast between clauses? If so, my doubt is on the clause before but, it says not in its specific which on rephrasing means bigger or broader;however, the second clause says the same broader, then how is this a contrast? Like in contras the LHS clause contrasts the RHS clause, here in my example both clauses are saying the same right? Then how is it a contrast?
Even though initial clause tells about provisions and second does on impact, purpose of but is semantically to contrast.
Can anyone explain me how the usage of but is used when both clauses mean same thing like in my particular example ?
If I am totally wrong above then what exactly is the purpose of but here? In cases of cause-effect relationship what is the but doing?
Edit1: FYI, my example sentence is can't be wrong I guess as it's from a standardised test
Edit2: I have seen this on Web in MacMillan dictionary but not sure if this definition fits, it says 1a. used after a negative for introducing what is true instead His death was not a tragedy, but a release from pain and suffering. In this particular example author is subjective, I believe. Can anyone explain on this? But in my example going by this definition bill doesn't or shouldn't have "specific" provisions but that isn't true. Or am I wrong?