THE INCAS WERE PROFOUNDLY RELIGIOUS.

The Incas gave cohesion to the Empire by practicing an inclusive form of religion. Having respect and understanding of the Spirit-Gods associated with places and objects and profound religious roots that let them have a clear view of the spiritual language of the new cultures conquered by them simply they absorbed into their pantheon the spirit-gods that governed the lives and lands of the conquered ones creating a powerful pantheon of deities.
The Inca deities occupied the three realms : Hanan Pacha, the celestial realm; Uku Pacha, the inner earth; Kay Pacha, the outer earth where humans live.
The Incas believed that the spiritual realm was governed by two sorts of gods: Greater Gods, who were individual, specific deities who ruled as a sort of pantheon, and the Lesser Gods or Huacas which were Spirits tied to a place or object such as a cave, river or boulder. Of the Greater Gods, only Viracocha (The All Powerful Creator God) and the Sun God were considered more powerful than the Thunder God.
The Inca Royal Family was venerated as semi-divine and had a very complicated system of ancestor worship.
The most important deities of the celestial realm (Hanan Pacha) besides Viracocha (The All Powerful Creator God) were Inti, the Sun God, and the moon goddess (Mama Quilla). The Inti Raymi was the festival of the Sun God (Inti) in the realm where humans live (Kay Pacha), and the largest and more important Inca Festival.
The Thunder God (Chuqui Illa), responsible for rain, hail, thunder and lightning also resided in the celestial realm was carried in the form of an idol by his priests during important rituals. During the Inti Raymi Festival The Thunder God got an equal share of the sacrifice animals (usually Llamas) along with Viracocha and the Sun.
 He was known as a man who lived in the cosmos and that he was made up of stars, with a war club in his left hand and a sling in his right hand. He used to dress in shinning garments which gave off the flashiness of lightning when he whirled his sling and when he wanted it to rain. The Milky Way was the river from which the The Thunder God would draw the water to make it rain. He was in charge of all the weather and thunderbolts, lightning, rain, hail, rainbows and other weather-related phenomena. His will was constantly under scrutiny. If a rain shower appeared in one town before passing somewhere else, the town was considered blessed. If an object was found to hold water when it rained, such as a stone or a piece of metal, it was said to have been specially blessed by the god and worshiped as a Huaca.
On the other hand, when The Thunder God was angry he brought disasters such as water shortages, floods or frost. When this happened, priests would communicate their auguries to determine what sort of sacrifice the god was demanding to restore the harmony of the land.
The Thunder God selected his priests in a very special way. Any boy born during a thunderstorm had been specially selected by the god for his priesthood. He took the priesthood when he had grown old and no longer have to work. This was a common practice for any priesthood discipline. Inca priests were older men who no longer did manual labor.