What was the significance of religion to the ancient Egyptians?

Religion permeated every aspect of ancient Egyptian life. The ancient Egyptians were polytheistic and assumed that different gods had powers specifically relevant to particular aspects of their lives. Different gods were assumed to be patrons of or associated with specific towns or regions as well as with certain aspects of life such as justice or fertility or professions (for example, Thoth was associated with scribes and writing).
The Egyptians had magnificent temples intended as houses for the gods; they acted as the center for a ritual calendar filled with festivals marking important times of the year. The temples and temple scribes were particularly important in religious rituals surrounding death. Pharaohs, the rulers of Egypt, were believed to be quasi-divine and had important ritual as well as civic roles. In addition to temples and state religions, there were types of popular religion or ritual, such as making offerings to the gods to ask for good crops or health. The Egyptians also consulted oracles to find out about the future.
The Egyptian gods were very concerned with Ma'at or harmony. One important element of living a harmonious life was gratitude. Thus gods served to reinforce morality and cultural norms.
The afterlife was quite important in Egyptian religion, and corpses were preserved and mummified so that they would be in good shape for the afterlife; elaborate tombs were built to house the mummies of pharaohs and important nobles. Various funerary goods were buried with people so that they would be well-supplied in their afterlives. 
The soul was judged after death. If it passed the judgment, it would have a happy eternal life in the lands of Osiris, but if it failed, it would be cast to the devourers and perish utterly. Thus much of people's religious behavior was aimed toward pleasing the gods in order to have a happy afterlife.