What is the Purpose of Thomas?

Since Stephen Carlson initiated a thread on the GThomas e-list the other day on Why Was Thomas Written?, I have been thinking a lot about this enigmatic text, stimulated further by the advent of April DeConick's postings on Thomas on The Forbidden Gospels Blog, and still further by the graduate course I am taking on Thomas here at Duke at the moment. One thing that seems clear to me about the purpose of Thomas is that we will only be able to make good sense of it if we take seriously what Bruce Lincoln calls "a seeming paradox" in its nature. He writes:

On the one hand, it proclaims itself to be secret, or to contain secrets, as in the Prologue . . . . But on the other hand, the text was widely circulated, and states that this is as it should be . . . . . This contradiction, however, can be accounted for by recognizing that Thomas, like Ptolemaeus' Letter to Flora and numerous other religious documents, is a text that is addressed at the same time to initiates and non-initiates alike. Thus, the fact that the Thomas-community possessed secret knowledge was proclaimed loudly to outsiders, but the nature of that knowledge and its true meaning were disclosed only within the community itself in a program of detailed instruction which must have lasted over a period of several years." (Bruce Lincoln, "Thomas-Gospel and Thomas-Community: A New Approach to a Familiar Text", Novum Testamentum 19 (1977): 65-76 [68-9])

Thomas points beyond itself. It is a text that demands explication, that encourages the hearer who has ears to hear to seek out what is hidden so that it will come to light.