In 1984, Winston says that he understands the how but not the why behind the Party. What is the why portion, and what page can I find it on?

The Party
uses its power to keep most people miserable and enforce the acceptance of lies. It keeps the
economy in a constant state of war. It keeps its Outer Party members under constant
surveillance. People have very few material goods, and what food they eat is of poor
quality.

knows the Party lies ceaselessly. He believes too that it could
make life better for people. The answer to why it doesn't lies, in my edition, on page 336.
Since pagination varies between editions, it might help to know that the answer lies on chapter
three of part three. Here, , who is torturing Winston in the Ministry of Love, explains the
"why" of Party policy to his victim. He says the Party, if it stopped the pointless
wars, could make life economically better for people. It could stop spying on people, and it
could stop altering the truth. However, it deliberately does not do these things because
power is its reason for being. O'Brien says:

"How does one man assert his power over another,...