Then the problem--how to express the condition of a man's body and soul, who, having for three days according to the story as Browning conceives it lived consciously in the eternal and perfect world, has come back to dwell in this world--was so difficult and so involved in metaphysical strangenesses, that it delighted him.
Of course, he carefully prepares his scenery to give a true semblance to the whole.

Karshish comes up the flinty pass from Jericho; he is attacked by thieves twice and beaten, and the wild beasts endanger his path; A black lynx snarled and pricked a tufted ear, Lust of my blood inflamed his yellow balls; I cried and threw my staff and he was gone, and then, at the end of the pass, he met Lazarus.

See how vividly the scenery is realised-- I crossed a ridge of short, sharp, broken hills Like an old lion's cheek-teeth.

Out there came A moon made like a face with certain spots, Multiform, manifold and menacing: Then a wind rose behind me.

So we met In this old sleepy town at unaware The man and I.
And the weird evening, Karshish thinks, had something to do with the strange impression the man has made on him.