I have always been amazed by how concise the language of the Qur'an is. One of the first times I noticed this was when I was reading a discussion somewhere about Baqara 2:
thalika al-kitabu la raiba fi ha hudan lil-mutaqeen
This verse has two possible interpretations: "This is the book, without doubt; in it is a guide for the pious" or "This is the book, there is no doubt within it; a guide for the pious."
I was reading about the relative arguments for supporting one interpretation over the other, when I realized that both interpretations are correct. The verse is structured specifically so two different ideas can be expressed in one sentence.
There are many other examples of the Qur'an's concise use of language. One other I have always particularly loved is in Al-Shams:
kaththabu ath-thamudu biTaghwaha
The Thamud rejected with insolence
itha anba'atha 'ashqaha
When their most wretched one was put forward
faqala lahum rasulullahi naqatallahi wa suqyaha
Then the Messenger of Allah said to them "the she-camel of Allah and her watering!"
fakaththabu fa'aqaruha fadamdama alaihim rabbuhum bithanbihim fasawaha
Then they rejected him and hamstrung her; then their Lord obliterated them for their sins and made them all equal
wa la yakhafu 'uqbaha
And He has no fear of the consequences
In five lines the entire story of the Thamud is related and the omnipotence of Allah subhanahu wa ta'ala is affirmed.