When Xander says, "It's a loop... like the Mummy Hand!" he is referring to Life Serial (2001), in which Buffy is caught in a time loop and must battle a severed, magical Mummy's hand.
Buffy's final speech, as she asserts her own and her friends' confidence and acknowledgment of the severity of what they are facing becomes a recurring trait of season seven. In fact, in later episodes both Buffy and Andrew poke fun at this fact.
Though it's not apparent when they first show up, the Potentials will redefine the nature of the series, in that the sheer number of eventual Potentials represents a major shift in style for Buffy's seventh season: taking in account the eventual total number of Potentials, in addition to the main characters, plus Giles, Faith, Principal Wood, Andrew, Caleb and the multiple manifestations of the First, the number of named characters grows to more than 20. This significant expansion of the cast means that screen-time is now divided among a great number of characters (some of whom are excluded from some episodes entirely), where previous seasons were always mainly focused on the original Scooby Gang (Buffy, Willow, Xander and Giles), with only a few more characters receiving notable amounts of attention.