What is the meaning of the following quotation from 1984? "The object of terrorism is terrorism. The object of oppression is oppression. The object of torture is torture. The object of murder is murder. The object of power is power. Now do you begin to understand me?"

While O'Brien is torturing Winston in the Ministry of Love, he acknowledges that Winston understands how the Party maintains absolute control over the population but demands that Winston answer his own question, which is why the Party wants power. After Winston offers a wrong answer, O'Brien proceeds to explain to him that the Party seeks absolute control for its own sake and is solely interested in power itself. Unlike the oligarchs and dictators of past regimes, Big Brother does not view power as a means to an end. O'Brien says it best by telling Winston,

Power is not a means, it is an end. One does not establish a dictatorship in order to safeguard a revolution; one makes the revolution in order to establish the dictatorship. The object of persecution is persecution. The object of torture is torture. The object of power is power. Now do you begin to understand me? (Orwell, 332).

O'Brien's comment essentially describes the singular motive of the Party, which is to maintain absolute control for eternity. This quote also exposes past and present authoritarian regimes for what they really are. Authoritarian regimes often attempt to justify their violent, oppressive tactics while disguising their true intentions, which is to maintain absolute power as long as they can.

This quotation explains the philosophy of leadership in Oceania but even more George Orwell's own understanding of authoritarian governments.
Orwell's 1984 was written in reaction to the rise of fascist and authoritarian governments in the twentieth century in Germany, Italy, Spain, and Russia. These movements originally practiced terrorism to gain power and when in power used tools such as oppression, murder, and torture as means of control. They tended to justify such behavior as necessary means to an end.
What this statement argues is that people who murder and torture are not fundamentally good people who act immorally out of necessity, but simply murderers and torturers. Authoritarian governments do not seek power as a means to another end, but because they want power. 
O'Brien, as a member of the Inner Party, understands this and actually exults in it, unlike Winston, who before being tortured believed the propaganda that these immoral acts were simply means to an end.