One of the most interesting things about the Nahuatl language, and thus the ancient Aztec mind specifically, is the concept of Duality which is all-pervasive.

So strongly were the Aztecs inclined to conceive in dualistic terms that when they wanted to endow an idea with maximum clarity and precision, they always isolated two of its qualities, employing what has come to be called difrasismo. Thus they evoked in the mind images that were not abstract and cold, but rich in meaning, fresh, vigorous, and dynamic.

The following examples of classic Nahuatl difrasismos are eloquent:

in cueitl, in huipilli--the skirt, the blouse; woman from a sexual standpoint.
in ahuehuetl, in pochotl--giant cypress, ceiba tree, authority, protective quality.
in chalchihuitl, in quetzalli--jade and fine plumes; beauty.
in atl, in tepetl--water and hill; a town.
topco, petlacalco--in the bag and in the box; a secret.
tlilli, tlapalli--black and red ink; writing or wisdom.
in topan, in mictlan--what is above us, the region of the dead; the metaphysical beyond.
Yohualli, ehecatl--night and wind; the transcendency of the Divine.
in xochitl, in cuicatl--flower and song; poetry, the only truth on earth.

Thus was the Nahuatl mind pervaded by Dualism. Ometéotl, the Dual God, invisible like the night, intangible as the wind, was the cause--or the effect--of this view of divinity, man, and the universe.

This, from the collective consciousness of a People the Spanish Conquistadors deemed "savage."

examples from Aztec Thought and Culture, a Study of the Ancient Nahuatl Mind
Miguel León-Portilla, University of Oklahoma Press : Norman, 1963

On Mexico and the Aztecs:

An Aztec father advises his son
Bernardino de Sahagun
Human Sacrifice and the Aztecs
Ometeotl, beyond time and space
Talk like an Aztec
Tlazolteotl, the Filth Eater
What points its finger at the sky?
Xipe Totec

Below the Line