the Party took over as they meet together in the room over Mr. Charrington's shop. Having another human being to love, be with, and protect rehumanizes Winston. He becomes a more compassionate human being, even able to see the fat, elderly prole woman who hangs laundry in the courtyard below as a lovable and beautiful person. In addition to regaining his humanity, Winston, through contact withO'Brien about a possible underground, gets a copy of Goldstein's book The Theory and Practice of Oligarchic Collectivism. This vastly increases his knowledge of the oppressive Party regime.

In part 3, Winston and Julia are arrested and separated. This part of the book concentrates on Winston's reconditioning to become acceptable to the state through torture by O'Brien and ends with him drinking alone at the Chestnut Tree Cafe. He is now a hollowed out human being who mindlessly worships Big Brother—except that he retains at least one loving memory of his childhood that the Party never got to and therefore never eradicated.

The three parts of the book track Winston's progression from angry and isolated outer Party member to loving human being to a person destroyed by the Party.

3 is a common number for writing and speaking organization.  I'm sure that you have had a teacher at some point assign a research paper.  The rough overview is always 3 parts: introduction, body, and conclusion.  More than likely that same teacher suggested that the body be made up of three main points.  If you take a super basic plot structure of novels and movies, you could break those plots into three chunks.  The introduction of characters and problems, the rising action/climax, and the resolution.  

1984 is broken into that three "act" structure. Not only that though, the number three is all over the place in the novel. It's a bit weird at times and often makes me think of conspiracy theories. Did you notice that there are three countries? Oceania, Eastasia, and Eurasia. Goldstein's book stressed that there existed only three kinds of people due to class structuring: high, middle, and low. 

"Throughout recorded time, and probably since the end of the Neolithic Age, there have been three kinds of people in the world, the High, the Middle, and the Low."

Winston works for the party, which by the way has threeslogans. His job there is to rewrite history. At one point he questions why the party would do such a thing. His thoughts were triggered because of the photograph he saw of Rutherford, Jones, and Aaronson -- 3 political dissenters.  

I like this quote:

"Behind Winston’s back the voice from the telescreen was still babbling away about pig-iron and the overfulfilment of the Ninth Three-Year Plan"

Crazy. A three year plan! Not to mention it is the 9th one, which is a multiple of three.  

Three main characters (Julia, Winston, O'Brien).  

The effect of having the entire novel broken into three parts is that it mirrors the repetition of three seen in the novel and gives readers a familiar structure by which the novel is written.  

It's instructive that the three-act structure of 1984 mirrors Oceania's tripartite class system. At the top of the pyramid, we have the Inner Party, the political elite, which makes up around 2% of the population. They are simply known as "The Party" because, for all intents and purposes, whatever they say becomes law. The members of the elite determine the State's often rapidly changing policies. They enjoy special privileges denied to everyone else, such as good food, comfortable living quarters, and the right to turn off their telescreens. That said, it can still be tough at the top, and Inner Party members are no less subject to brutal torture and punishment than anyone else should they be foolish enough to step out of line.

Below the Inner Party, we have the Outer Party, of which Winston and Julia are members. These are the regime's functionaries, expected to carry out the Inner Party's directives to the letter. They are also expected to display exemplary ideological zeal, participating in such public acts of loyalty to the regime as the Two Minutes Hate. Unlike the Inner Party elite, they live in squalid conditions, expected to exist on minimal rations and subjected to almost constant surveillance by the State.

Finally, we have the Proles, the working classes, who make up 85% of the population. The State doesn't think they have much in the way of a revolutionary consciousness, so they're pretty much left to their own devices, fed upon an endless diet of bread and circuses ("prolefeed"). Winston, however, believes that the Proles constitute the only real hope for change, as they're largely free of any ideological hang-ups; they're doers, not thinkers.

Three is a Magic Number:

• 3 act structure: beginning (problems), middle (climax), end (resolution)
• 3 geographical settings (Oceania, Eastasia, Eurasia)
• 3 types of people according to Goldstein's book:

Throughout recorded time, and probably since the end of the Neolithic Age, there have been three kinds of people in the world, the High, the Middle, and the Low. They have been subdivided in many ways, they have borne countless different names, and their relative numbers, as well as their attitude towards one another, have varied from age to age: but the essential structure of society has never altered.

• The three slogans of the Party:

1. WAR IS PEACE
2. FREEDOM IS SLAVERY
3. IGNORANCE IS STRENGTH

• 3 main characters (Winston, Julia, O'Brien)
• 3 is often used as a literary device to provoke a feeling of unnaturalness, as twos are much more common in nature (limbs, hemispheres, eyes, etc).  We realize that O'Brien is third wheel, unnatural.
• 3 verb tenses: PAST, PRESENT, FUTURE.  Winston has a hard time distinguishing one from the others.
• The Party has rolled out nine "3 Year Plans"
• 3 political prisoners (Rutherford, Jones, Aaronson)

It is quite common for plays to have a three act structure, and Orwell applies it to 1984. The first act normally encompasses the exposition; the second act, the rising action; and the third act, the climax and resolution. Adopting this structure feels particularly appropriate as it allows us to accompany Winston Smith on his long and tortuous journey, not quite knowing where it will lead, but certain nonetheless that we can expect a suitably dramatic climax.

Appropriately enough, this journey passes through three distinct stages: Winston as humble state functionary; Winston as rebel against the regime; and Winston as the physically and mentally destroyed victim of torture who's learned to love Big Brother.

It is also notable that the number three comes to have a great deal of significance in the book itself, cropping up in numerous contexts. There are three world powers (Oceania, Eastasia, and Eurasia), three main characters (Winston, Julia, and O'Brien) and three main slogans ("War is Peace," "Freedom is Slavery," "Ignorance is Strength.")