A lot of people seem to have issues with the inconsistencies in the slayer line on the show, so I went through the show to try and find a reasonable explanation, and I think this pretty much covers it.
Here’s a timeline of events that fall into this theory:
PROPHECY GIRL (1x12)
Buffy dies, passing the slayer line on to Kendra; Buffy is no longer ‘The Slayer’, just a girl with slayer powers.
BECOMING PART 1 (2x21) Kendra dies, the slayer line is passed to Faith.
THE GIFT (5x22) Buffy dies, the slayer line is unaffected.
Willow calls Buffy the ‘warrior of the people’ (AKA the Slayer) in her resurrection spell. Buffy is revived as The Slayer, splitting the line in two.
SMASHED (6x09) Because Buffy is technically The Slayer again, the demonic aspect of her strength is ‘surfaced’, explaining why Spike’s chip doesn’t fire off.
SEASON 7 The slayer line splitting (Buffy’s resurrection) causes the ‘instability’ that the Bellajoxa’s Eye tells Anya and Giles about. This creates an opportunity for the First to rise.
Hopefully this helps to fill some of gaps left by the writers.
This is the great era of shamanism, and what is shamanism but philosophy with a ‘hands on’ attitude? Philosophy not made around a campfire, but philosophy based on the acquisition of extreme experience. That’s how you figure out what the world is. Not by bicycling around in the ‘burbs, but by forcing extreme experience. The reason people refer to psychedelic endeavors with the vocabulary of travel—taking a trip and so on—is because that is an extreme endeavor. It’s the same endeavor. It’s the leaving behind of the values of your own culture. Take nothing but a change of clothes, fly to Benares, and take up residence at Dashashwamedh Ghat among the Charas Shaivites, and I guarantee you, whether you resort to psychedelics or not, you will experience boundary dissolution, a reorientating of categories, and a reframing of your perspective on your life and your being. So extreme experience is the necessary key. This is true in all forms of endeavor. If you want to understand the atom, you have to smash it. Sitting around looking at it, it will never yield its secrets. You have to smash that sucker to bits and then collect the pieces and then examine exactly how it all came apart. In the same way, and without going too far afield for the pun, we must smash ordinary consciousness—get smashed—and then look at the pieces flying in all directions.