Purification for the Sake of What?

Majjhima Nikaya MN24.15. Rathavinita Sutta: The Relay Chariots (รถวินีตสูตร)

“So too, friend,
(1) purification of virtue is for the sake of reaching purification of mind;
(2) purification of mind is for the sake of reaching purification of view;
(3) purification of view is for the sake of reaching purification by overcoming doubt;
(4) purification by overcoming doubt is for the sake of reaching purification by knowledge and vision of what is the path and what is not the path;
(5) purification of what is the path and what is not the path is for the sake of reaching purification by knowledge and vision of the way;
(6) purification by knowledge and vision is for the sake of reaching final Nibbaana without clinging.

It is for the sake of final Nibbaana without clinging that the holy life is lived under the Blessed One.”