The talked mercy and love. The most important aspect of the religion was the complete lack of human sacrifice. According to Aztec religion Quetzakoatl was the god of thunder. Because the natives where ignorant of firearms, loud booming weapons of death where seen only as tools of a god. Montezuma was completely demoralized by the thought of an ancient god waging war against him. When his advisors told him to fight back he replied "What good is resistance when the gods have declared against us?" There were several aspects of Cortes that proved him not to be the great god Quetzakoatl. Cortes did not speak Nahuatl. It was hard to believe that Quetzakoatl had forgotten his own language. More importantly, Cortes spoke of a greater power above him. It was impossible for a great god to have a higher king. This confusion allowed for Montezuma's capture as well as the downfall of his army.
The small army Cortes had too demonstrated many godly attributes. Their firearms intimidated Montezuma's men. The greatest weapon they brought with them was disease. The European community had developed immunity to smallpox. This was used not only as a biological weapon but as a demoralizing factor. This disease alone wiped out about 95% of the population of Mexico over the course of 80 years. Although war wasn't long enough to for the disease to numerically affect the Aztec army, its presence helped provide Cortes's men with godly attributes. The Aztecs saw this disease as a mysterious ailment that affected only them. The psychological effect this had on Montezuma's men was substantial. While many believed that Cortes himself was the reincarnation of Quetzakoatl his men too were seen as an invincible fore from the gods. This as well as the advanced armory of the European soldiers gave them an immortal appearance.
Technologically, Cortes's men had a great advantage over the Aztec army. The Spanish armor was comprised completely of steel.