On pg. 16, Orwell says:
Curiously, the chiming of the hour seemed to have put new heart into him. He was a lonely ghost uttering a truth that nobody would ever hear. But so long as he uttered it, in some obscure way the continuity was not broken. It was not by making yourself heard but by staying sane that you carried on the human heritage. He went back to the table, dipped his pen, and wrote:
To the future or to the past, to a time when thought is free, when men are different from one another and do not live alone — to a time when truth exists and what is done cannot be undone: From the age of uniformity, from the age of solitude, from the age of Big Brother, from the age of doublethink — greetings!
He was already dead, he reflected. It seemed to him that it was only now, when he had begun to be able to formulate his thoughts, that he had taken the decisive step.
Winston's journaling is not a written record for the future, but a means to make sense of the current dystopia: "He was a lonely ghost uttering a truth that nobody would ever hear." His writing is a way to counteract the "doublethink," his first step toward freedom. Winston has been in such a vacuum--cut off from history and intellectual thought--that he is trying to form a community of one here. He knows if he can come up with one thought on paper, just one, that he can "be able to formulate his thoughts, that he had taken the decisive step." He sees himself as being dead for a long time, but this first step toward intellectual awareness can resurrect him from the ash heap of history.
I don't like pop culture analogies, but Winston is a lot like Neo from the Matrix when he says, "There is no spoon." If Winston can see past the doublethink (The Matrix), then he can be alive for once in his ghostly existence.