Exact meaning of Ditthivisuddhi (3rd purification) Is ditthivisuddhi (the 3rd purification) only the purification of the illusion of 'self'; 'I'; 'me'; 'mine'?
Understand that mental and physical process and the world at large is not in our control and is changing. So any notion of regarding one self will not be in line with expectations and also would lead to comparison hence misery. (3 Marks of Existence) Further the understanding of the 4 Noble Truth and Dependent Origination.

See: Rathavinita where this is initially covered.