When Angel was attacked by a Lubber Demon in the library, it was wielding a Hunga Munga, an African blade. It was previously used by Buffy Summers in Anne (1998).
When Angel says he can relate to love and how it might destroy the world, he is referring to the events of Surprise (1998), and the culmination of said events in Becoming: Part 2 (1998).
The first episode in Angel that introduced the theme of Angel being a "Champion," affirmed in this instance by the Host.