You are trying to understand and Infanite God..with a finite mind..its impossible.. It is like me telling you to picture in your head a new color no one has seen before.. The whole thing with if God is perfect how can everything he did be so screwed up. Well God is a perfect being..his plan was perfect..Its Humans that screwed up..but that initself was part of the plan..if Saul hadn't messed up..it wouldn't of made room for David... It's so uncomprehendable you shouldn't even try to understand it..it's like teaching a child Theorys of Relativity...he just wont understand it.