The big bang, unlike theology, tells us why distant objects are more red than close objects, why we can't see anything further than ~13bil light years away, why there is microwave noise everywhere, etc. The mathematics that describe all those things imply certain things about earlier cosmological history.
Yet. As we gather evidence ever closer to the actual moment of the big bang (such as the possible recent discovery of a particular kind of polarization in the CMB), we might figure out ways to prove or disprove theories about what might have preceded the big bang.
As I understand the process, theoreticians will invent mathematical constructs that explain everything we have measured already, plus make predictions about something else we can test. If all of the testable predictions are verified, then we are somewhat safer in accepting any untestable predictions of the same model. Then, an expanded mathematical theory will be devised with new physical tests, etc. ad infinitum.
Before there can be answers there must be questions. Theoretical physicists come up with new possible questions that are later narrowed down and answered by experimentation and observation.
The fact that there is an ongoing process of scientific discovery that has continued unabated, while theological knowledge remains stagnant or even decays, is alone enough reason to give credence to even the most far-fetched theory that might one day have a hope of being tested.
To summarize, hard science like theoretical physics is not about beliefs or answers or end goals, it's about a continual process of expanding knowledge, guided outward by the imaginations of theoreticians.