Why would an omnipotent and omnipresent being who is love incarnate need to offer himself as a blood sacrifice to himself to do something he apparently wants to do?
Sacrifice entails an offering to a higher power - if God is all powerful, why the charade of the sacrifice, and if not - who is he sacrificing too?
http://tvtropes.org/pmwiki/pmwiki.php/Main/FridgeLogic
http://tvtropes.org/pmwiki/pmwiki.php/Fridge/TheBible