Hi, people, this is a fairly simply one; it took me 38 seconds which would probably mean a solid 1:00 on an actual GMAT.
It may just be me, but I feel some passages are simply easier to read, comprehend, and get the gist of compared to others. I daresay that this passage has been written to be reader-friendly and is designed as a simple question of theme beyond anything else. Clearly, this is not a question of logic or assumption.
To give you all an idea how I read this - and what I focused upon - look at the portions below.
A law that is not consistently enforced does not serve its purpose. Law without enforcement is not law; it is merely statute—a promise of law. To institute real law is not merely to declare that such and such behavior is forbidden, it is also to punish those who violate that edict. Furthermore, those who enforce law must punish without favor for their friends or malice for their enemies. To punish only those one dislike while forgiving others is not to enforce law but to engage in the arbitrary and unjust exercise of power.
It becomes fairly clear that the author has a strong definition for what he or she considers (real) law. Picking those definition markers should become clear reading the question The main point of the passage is that instituting real law consists in - I understand people have their own way with approaching CR, but reading the specific question being posed can help you focus on what to look for in the passage. A few seconds can't hurt to alter your process a bit sometimes. It almost certainly would help in a question such as this.
Coming back to the answer choices.
The main point of the passage is that instituting real law consists in
(A) the exercise of power
Nope. This seems to be a trap for those who might confuse the exercise of power with consistently enforced. The two have slightly different meanings. But rather than getting bogged down with the fine details, simply ask yourself: is this the main point of the passage? There seems to be so much more. Rather than debate with yourself, keep this one if you must and move on for a better answer you are all but sure will soon present itself.
(B) authorizing the enforcement of punishments
There is nothing about authorizing the enforcement of punishments. At best you could say this only refers to one part of the author's definition of real law. We need something more general, something that encapsulates all the author is saying. Give this one a yellow flag, if you are feeling unsure.
(C) the unbiased punishment of prohibited behavior
Bingo. This actually hits two things simultaneously. The unbiased punishment -- of (all) prohibited behavior. It pretty much encapsulates everything the author is trying to convey. Don't try to fight the answer. Compare it to the alternatives and judge which one is better.
(D) understanding the purpose of law
Completely nonsensical! The main point of the passage is that instituting real law consists in understanding the purpose of law? This is a freebie elimination.
(E) clearly defining unacceptable behavior
Unless, I missed something, the author does not mention this in his or her definition. So, it's out of bounds from all consideration just there. I imagine this answer choice is to trip up those who add some of their own story into the passage. Also, remember, go back to the specific question. Is this the main point of the passage? The passage seems more intent on the punishment meted out by law rather than the formation of law itself. (Looking now I can see why this answer choice was given: To institute real law is not merely to declare that such and such behavior is forbidden. This, however, flies in the face of what the author intends and is probably intended to trip up those who may mistake a negative for a positive definition attribute. Perhaps I skimmed over that a little because I was looking for positive definition markers rather than negative or out of bounds ones. Interesting. Keep an eye out for this kind of thing, though. Had the question been posed a little differently not knowing this negative definition might have made all the difference in getting it correct or incorrect.)