To prepare himself, he takes full control of the Fox's powers, discovering that his father and mother sealed the Fox inside him so Naruto could use its power to defeat Tobi, Pain's superior who was responsible for the Fox's attack to Konohagakure.
He takes full control of the Fox's powers. This was to prepare himself. His father and mother sealed the Fox inside him. This was to prepare himself. Naruto could use its power to defeat Tobi. This Tobi was responsible for the Fox's attack to Konohagakure. He was discovering this. Tobi is Pain's superior.