1-Ivan suggests that the GI and the other priest will take on the sins of mankind. They will lie and do other sinfull(enslave mankind for example) things so that mankind will know forgiveness for whatever they do. Ivan suggests that they will feed the weaknesses in man that Jesus denied them when he refused the temptations, trying to give us the free will to follow him.
2- The GI says that Jesus misunderstood what man really needs. He said that Jesus thought he could fix mankind with free will, pride, and courage. But that was not what man needed. The GI believes that men are like beast, almost, they need food to satisfy and someone to call master and they will be happy.
3- The GI and the priets will take on the responsibility of freedom for mankind(enslavement). The GI says that freedom scares man. So the GI will take away their freedoms in HIS name and then will give them al they need to be happy.
4- I think that suffering is similar to the whole tree of knowledge thing. You want to not be kept in the dark,but with it comes things you wish you didn't have to know, to know freedom we must know the struggle to achieve it aswell.If you don't have to fight for something it probably isn't worth having.