The title is "the Secret of the Pure Light", so you naturally think that they'll reveal why one of the Band of Seven has a totally different personality now, and has no memory of his past or that he was one of the band of seven, and why his Shikon Jewel shard is totally free of any shadows. But when you actually see the episode... it's far less than what you had expected. In fact, the title is extremely misleading. They don't reveal any secret, or even tell you anything usefull or important. It's just basically: Inuyasha-"I'll kill them!"
Suikotsu-"what are you talking about?"
Kikyo-"Pure, is impure. Impure, is pure. Good, is evil. Evil, is good."
If what Kikyo said is the secret, they could have at least told you that's what she was mumbling about. Basically, it had it's good points, but overall, it was pretty much like school books. They never seem to supply enough information or explain the information they give you well enough so you actually do understand it, so by the time your done, your sitting there, scratching your head going "...huh?"