Frampt gives you the Lordvessel to move around more freely, letting you become powerful enough to stop Gwyn, and Kaathe reinforces this by stating that the Lord of Cinder "resisted the course of ...

Well, he's got a chum. First of all this meeting will only be possible if you have never let Kingskeeper Frampt take you to the entrance to the Kiln of the First Flame, where you place the Lordvessel.

As Frampt has warned me, the fortress is a "deadly house of traps," but that's rather underselling the sheer number of death-dealing devices this 'Sen' has stuffed into their Lordran vacation rental.