The verb tara can mean sensory seeing, yet context may extend its force to awareness or comprehension. Bringing the addressee imaginatively before a scene intensifies the discourse.
«وَلَوْ تَرَى إِذْ وُقِفُوا عَلَى النَّارِ»
If you could see them as they are stationed before the Fire.
The scene belongs to the future, but idh and the vivid visual framing make it present to the listener’s imagination. This is the rhetorical aim of portraying a future event as if seen directly.