The seven purifications come from a discourse in which they are compared to seven relay chariots, each taking the traveller only as far as the next: purification of virtue, of mind, of view, by overcoming doubt, by knowledge of what is and is not the path, by knowledge of the way, and by knowledge and vision. Buddhaghosa organized his account of wisdom around them.
Seven purifications
The stages of the Buddhist path, from virtue to knowledge and vision, likened to a relay of chariots.
Also: satta visuddhi