Writing an introduction to ancient Egypt temples is considerably more difficult then examining any specific structure, for a number of different reasons. First of all, the term "temple" is misleading, and secondly, the term covers a huge variety of different structures that evolved over such a vast period of time that many people have a difficulty comprehending just how long a time this period spans.
For example, think of the Roman Coliseum (in Rome). It is almost 2,000 years old, and most of us would think of it as very ancient. Yet, when the Romans first came to Egypt, they were awe struck by Egyptian temples, some of which at that time were already more ancient to the Romans, then the Roman Coliseum is to us. So we must consider the effect that these temples had on the ancient Egyptians. Imagine the feelings of old tradition and holiness felt by a young priest when he first enters St. Peter's Cathedral in Rome. How must a young Egyptian priest felt as he strolled the courts of the much more temple of Heliopolis, which was much more ancient to him then St. Peter's would be to a young priest of today.
Webster's New World Dictionary defines temple as "1. a building for the worship of god or gods, and 2. A large building for some special purpose". For the second definition, they provide the example, "a temple of art". Neither of these definitions fit the ancient Egyptian temple very well, and yet, almost every religious structure in Egypt outside of the various types of tombs are almost always referred to as temples.
Certainly some of these "temple" structures do embrace both of Webster's definitions. In fact, it is difficult to imagine most any large, ancient building not falling under the second definition, including palaces and governmental buildings. However, our modern readers are more likely to think in terms of the first definition, that of a temple being a place of worship. However, this definition is simply too limited to fit even the structures that many modern Egyptologists better define as a "god's mansion". Even these temples sometimes had many other functions, acting sometimes as fortresses, administrative centers and even concrete expression of propaganda or royal retreats. However, it is difficult to define some other religious structures that are called temples as houses of worship or "god's mansions". They may have other political or all together different purposes.
It was the ancient Egyptian temple that received endowments. It was the mortuary temple and the cult of the dead king that funded the entire pyramid complex of the early kings, for example. Temples owned land, livestock and received donations, sometimes including the spoils of war, in order to support often large populations of priests, workers, and sometimes even an entire support town.
The Temple of Karnak today remains the worlds largest religious structure, but what is perhaps even more interesting is that it might not have been, or indeed was probably not Egypt's largest temple. Certainly the Temple of Ptah in Memphis, though for the most part completely gone today, may have been larger. It was older, and located in what was often the capital of Egypt, and more often the administrative center of the ancient country. Other temples in the Nile Delta might have been just as large as Karnak, if not larger.
Sites such as Karnak, Dendera and Kom Ombo would most likely fall under the category of "god's mansion". They were more then religious "temples" however. While the god may certainly have been worshiped in these temples, it was also his symbolic home, if not considered his physical residence, and the functions of the temple were as much to serve his or her symbolic physical needs as they were for the god's worship. There was probably little or no "preaching" as such, or carrying the message of the god to the people by priests associated with these "temples". Rather the efforts were directed inward, towards the care of the gods.
Also, though we often make a very specific distention between mortuary temples of kings, for example, and temples such as Karnak, they were actually very similar. Kings were considered gods, and after their death, they required a "mansion" and the same attention as other gods. Both regular and mortuary temples served to keep the name of the king or god alive.
The real distinction, religiously, seems to be in regards to structures that might not so easily be defined as "god's mansions". Nefertari's temple at Abu Simbel was certainly dedicated to the goddess Hathor, it would seem. But this also seems to be a situation where a "god's mansion" was built as much for political as for religious purposes. These great monuments at Abu Simbel, consisting of her temple, and the larger temple of her husband, Ramesses II, were not just temples. They were also reminders of Egypt's greatness to her southern neighbors. Other structures hardly fit within the "god's mansion" category at all. For example, Sed-festival Temples that celebrated the king's jubilees seem to have had a completely different purpose than "god's mansions", and ka Temples provided a residence not to the dead king, but for his soul.
Nevertheless, for convenience, we will refer to most religious structures other then tombs as temples in the remainder of this reference.
Dynastic era temples may be found throughout Egypt, though the ones that have survived time are mostly in the south. They were built for many different forms of worship, as well as other purposes. Some were major temples dedicated to major deities, while others were dedicated to a number of different deities. Some were mortuary temples, where the temple was dedicated to the deified dead king, and where he was worshiped and cared for by his cult. There were also valley temples, which were often no more then monumental gateways connected to the king's mortuary chapel by a causeway. There were all manner of specialized temples, such as Sed-festival temples, ka temples, sun temples, coronation temples and others.
Many of Egypt's temples became complex systems of buildings, added to by generations of pharaohs over sometimes thousands of years. Such temples include those of Luxor and Karnak, but others long destroyed, such as the Temple of Ptah. In fact, there are any number of northern temples, though long gone, that would have rivaled the southern temples that we most often visit today.
Most Temples had some sort of organized structure that evolved into a traditional, if somewhat varied floor plan. For example, the mortuary temple of 5th Dynasty kings invariably had an outer section and an inner sanctuary. The outer section would consist of an entrance corridor, followed by an open columned courtyard. Often, the pillars were inscribed with the king's name and title, and the northern columns would have scenes oriented to northern Egypt's symbolic gods, with a similar arrangement on the southern columns. Various additional minor chambers might also exist within the outer section, including, for example, an entrance vestibule or a guard station. Between the outer temple and the inner section there was usually a transverse corridor, and in the center of the long, west wall a doorway lead to the inner sanctuary of which the front section consists of a chapel with five niches for statues. Behind the chapel would be an offering hall, notable for a false door on the west wall that faces the pyramid, and before the door, an offering altar. Within the inner sanctuary there might also be additional rooms, such as vestibules and antechambers. Associated with both the outer and inner sections of the temple would be storage and other annexes to one side or both of the main temple components.
Non-mortuary temples often also had courtyards, chapels, offering halls, vestibules, antechambers, just like the mortuary temples. They tend to vary considerably in their style and elements, though temples built for specific gods tended to be more uniform (though not always). One of the major differences between mortuary temples and others was that the non-mortuary temples were very often added to, built upon and even usurped by various kings. Though in rare cases a mortuary temples, such as that of Djoser at Saqqara, became places of high holiness, and were built upon by later kings, most mortuary temples were never added to or usurped. They therefore most often were much more simple than major non-mortuary temples.
Latter temples took the form of fortresses, with massive entrance pylons and enclosure walls, huge courtyards, columned or pillared halls and inner sanctuaries.