Each lord had in his house a chapel with composer-singers of dances and songs, and these were thought to be ingenious in knowing how to compose the songs in their manner of meter and the couplets that they had. Ordinarily they sang and danced in the principal festivities that were every twenty days, and also on other less principal occasions….
As we see in the quote above, music was important enough that the nobles often had their own band, song writers and studio right at home.
The gods Ometeotl, Tlaloc, Huitzilopochtli and Tezcatlipoca were all honoured in song.
These songs could be sung at special occasions, accompanied by special ritual dances.
These songs were specifically sung at times of battle.
Of course, Aztec music also included the more lighthearted songs, and songs of everyday life.
The cantares were only for religious ritual, but there were plenty of more universal songs.
Source: New Aztec history facts