Religion played an important part in Aztecs' lives and was very complicated because they adopted many aspects of the people that they conquered. They had three dominate gods: Huitzilopochtli ("hummingbird wizard," the native and chief god of the Tenochca, Huitzilopochtli was the war and sun god), Tezcatlipoca ("Smoking Mirror," chief god of the Aztecs in general), and Quetzalcoatl ("Sovereign Plumed Serpent," widely worshipped throughout Mesoamerica and the god of civilization, the priesthood, and learning). Below these three gods were four creating gods who kept themselves from the human world. Under these were a large number of other gods, the most important were Tlaloc, the Rain God; Chalchihuitlicue, the god of growth and Xipe, the "Flayed One," a god connected with spring. The Aztecs worshipped about 1,000 gods, but the the sun god was the most important. Religious ceremonies were held in a temple called a teocalli. The temples had pools for ceremonial cleansing, gardens, living quarters for a priest, and racks to hold the skulls of victims.
The most prominent part of the Aztec religious life was the role of human sacrifice. It was practiced in all of Mesoamerica, but the Tenocha used sacrifice on a grand scale. We don't know a great deal about the details, but we can successfully reconstruct its general character and justification with a high level of accuracy. In Mesoamerica, the religious concept was that the gods provided things for humans only if they were nourished by human beings. The Mayan priests would nourish the gods with their blood caused by piercing their tongues, ears, extremities. Sacrifice had other practices like prayer, offerings of food, sports, and even dramas.
The Aztecs used all of these sacrifices, but they also developed the idea that the gods were nourished better by living hearts of captives. If the captive was brave, the better the sacrifice. The Aztecs thought their gods would turn against them if they were not given human sacrifices. This belief led to many wars to find victims both captured in war and those paid to the Aztecs as tribute by the people who were conquered. Human sacrifices were made to make the sun rise the next day. They believed that if the sun god were not fed human hearts and blood the sun would not rise and the world would end in disaster. The Aztecs believed that their special purpose in life was to delay that destruction. They sacrificed to the gods to avoid destruction for as long as possible. On God's Feast Day, slaves were killed for the gods.
Human sacrifices were also to the sun and earth for food to grow. The number of victims to the gods was enormous. During one famine, the Aztecs sacrificed over 10,000 people. Most of them had been captured in war.
Some ceremonies were small, with the sacrifice of a slave to a minor god. Others were very spectacular, involving hundreds or thousands of captives. Aztec history claims that Ahuitzotl (1468-1502), the ruler before Mocteuzma II, sacrificed 20,000 people after a battle in Oaxaca ("O-a-sha-ka"). Large or small, the sacrifice was always handled the same way. Four priests held the victim on an altar at the top of a pyramid or temple while the preceding official made a cut below the rib cage and pulled out the living heart. The heart was burned and the body was pushed down the steps; a brave or noble victim was carried down the steps. The most brutal sacrifices were those honoring the god Huehueteotl. The victims were gven a drug, dragged with hooks to the platform, their living hearts were cut out and thrown into the fire on the ceremonial platform and then the body was thrown into the fire.
The Aztec culture had an end-time belief which created an urgency to the sacrifices. The believed that they could influence the conflicting forces of creation and destruction by the rituals of sacrifice. The Aztecs, like the Mayans, believed that the universe had been started five times and come to an end four times; these five times were called a Sun. The first was Four Ocelot (because it began on the date called Four Ocelot). Tezcatlipoca (Smoking Mirror) controlled this universe and became the sun disk. This first age was destroyed by jaguars. The second age was Four Wind, dominated by Quetzalcoatl (Sovereign Plumed Serpent); men were changed to monkeys and the world was destroyed by hurricanes and tempests. The third age was Four Rain, dominated by Tlaloc (the rain god); the world was destroyed by a rain of fire. The fourth era was Four Water and was dominated by Chalchihuitlicue (Woman with the Turquoise Skirt); the world was destroyed by a flood. The fifth era, the one we live in now, is Four Earthquake, and is dominated by Tonatiuh, the Sun-God. This age is believed to end in earthquakes.
The Aztec religion was also based on the calculations of time. There were several calendars where each day had two gods that could either bless or punish the people. These deities were then represented in the calendars of the Aztec, two of which were the Day-Count and the Solar Year. By a series of calculations based on astronomy, the people could figure out how to act to get the best out of ach day.
Art had a part in their religion. The Aztec scribes and priests drew pictures that told about their gods and recorded religious events with hieroglyphics and even number symbols.
The Aztecs had a strong belief in life after death. The way the Aztecs died was more important than the way they lived and this was the determining factor on whether they would go to the sun god or go to the dark underworld. If a person died a normal death, his or her soul would have to go through the nine lives of the underworld before reaching Mictlan or the land of the dead. A warrior who died in battle or a woman that dying bearing a child would go straight to the sun god.