In the background you'll see a pagan temple being rebuilt. Leonardo was making a subversive comment here. It seems the patron who commissioned the painting was upset by that and sacked Leonardo from the project. He then paid someone else to paint over the pagan temple. What you're seeing above is the restored Leonardo version.Why was it unfinished?
I see art appreciation is not your forte .though I think he was obviously way more than an artistIts a ghastly painting created by a thoroughly overated homosexual artist who effeminized everything in sight to the point of ridicule.
True to form his religious work is entirely devoid of any grace including the awful Last Supper on which millions was spent in restoration.
Do not go to see it.