If any of your women are guilty of lewdness, Take the evidence of four (Reliable) witnesses from amongst you against them; and if they testify, confine them to houses until death do claim them, or Allah ordain for them some (other) way. (4:15)

Can someone please explain this verse?

Moreover, to prove a rape, four witnesses are required. Is that possible, specially in the contemporary world? And if there indeed are four witnesses (how big an assumption is that, btw?), can they not be pressed for charges of being an aid to the crime and the criminal? Witnessing and not stopping the crime?