It is essentially used to corrupt and restrict the mind. The language is designed to make the population conform to the beliefs of the government, and makes it impossible for them to perceive anything other than English Socialism. If the word 'freedom' doesn't exist, how will people think of freedom or realise that they are being controlled and repressed by the Party?
The Party seek to make thinking completely pure - void of rebellious thoughts. This means that by 2050, when Newspeak will have completely replaced English, thoughtcrime will become impossible.
The concept of Newspeak