This aspect of Christian theology makes no fucking sense. First of all, why should anyone pay for the wrongdoings of another? What kind of justice would it be, if you were thrown in jail for someone else committing a theft, rape, or murder? It wouldn't be just at all. Second, why would God need to send himself through a mortal incarnation, and then have that mortal incarnation die from Roman torture so that He can forgive his own creation? He's supposed to be omnipotent and omniscient. He can do all of that without all of these extra steps.
Islam's theology is at least logical, even if some of their social rulings don't make sense (like why the prophet can have ten wives, but everyone else is limited to four).