In essence, what we do not know will manifest as what we do know.

This is not only for assurance, but so as not to scare the living daylights out of us.

Take for instance the fact that in truth we genuinely do not know what Jesus may have looked like... What if (hypothetically) "he" was a grossly disfigured female with 4 arms and 6 legs. Would we want that to manifest before us? No! If we saw that, we would run screaming for the hills and likely end up on strong meds in an asylum.

Regardless of whether it was genuinely Jesus, or just a play of light - if it gave people a morale boost (and in hospitals that is where it's needed most) then that is all that matters.