The cultural and historical significance of this sight cannot be overstated, and needn't be stated here. Wiki it if you have questions, I'll just say that, although a Protestant Christian in a large group of obviously tourists, I felt drawn into the experience of worship and supplication rather than repulsed therefrom. Practical points: you'll go through security before going in, so if you're in the habit of carrying a pocket knife or pepper spray leave it behind; they provide kipas if you do not have a head covering; they probably will not get onto you for dressing immodestly "by their standards" but you will feel out of place, so it will help the experience to dress in at least pants and a shirt with buttons. Other than that, I'd just say try to appreciate how genuine the expressions of faith are.
This review is the subjective opinion of a TravelPod member and not of TravelPod.com.