Wicca does have its own theology. Or, more accurately, it does according to most introductory books on the subject. Many even refer to it as the religious aspect of Witchcraft, which it isn’t (at best, it’s one of the religious aspect of Witchcraft).
Taking a beginner’s guide at random from the shelves, Jeremy Kingston’s "Witches and Witchcraft" [Danbury Press, 1976] states that: “Modern white witches worship the Great Mother, the Earth Mother… [and] also the Horned God” Kingston was writing a goodly amount at that time, but that sort of categorical statement can still be found on any number of Internet introductions to Wicca.
Most modern Wiccan primers, however, are more understanding of the path’s diversity. In Tony and Aileen Grist’s "The Illustrated Guide to Wicca" [Godsfield Press, 2000], the picture is painted less brashly: “Most Wiccans believe that divinity is both male and female. For some, that means acknowledging a single goddess and a single god. For others, it means worshiping a number of gods and goddesses selected from Pagan pantheons.”
The authors go on to mention that Wiccans, being pragmatists, don’t tend to get hung up on the issue of how “real”, if at all, these invisible friends are.
A common Wiccan approach is the belief in numerous Gods and Goddesses. Polytheism may be inclusive (that is, all deities are awarded equal credence), preferential (one pantheon might be given more respect than others) or exclusive (certain pantheons may be excepted from belief).
This last one, it’s not uncommon, for example, we hear polytheistic Pagans stating, perhaps with questionable logic, that they disbelieve in Satan since he belongs to the Christian pantheon, rather than the Pagan).
Out of the many curious aspects of contemporary Witchcraft is that you can never be entirely sure what anyone else means when they use the two “W” crucial words: “Wicca” and “Witchcraft”.
For years, people have been telling us that one or the other, or both, of these phenomena are among the fastest growing movements in the world, but they frequently get evasive when asked to define the terms. Matters get murkier still when non-Wiccan and non-Witchy Pagans (some of whom use magic and some of whom don’t) are flung into the statistical cauldron.
For most of the last half-century, a magazine called Witchcraft could equally accurately have been named Wicca. Most practicing Witches freely acknowledged the debt they owed to Gardnerian Wicca in terms of both magical theory and practices.
Today, however, other types of Witch are proliferating, most notably those who approach Witchcraft primarily as a craft, rather than as a form of Pagan religion. Their principal interest is in effective spell craft, rather than ceremony.