It stems from what happened in the Garden of Eden. What took place there was more than spiritual separation, in everyway possible we had lost our connection to GOD.

Jesus' penalty had to completely cover all aspects of our sin, flesh, soul, emotions, spirit, because as humans we are more than just spiritual.

For centuries man has tried to correct our separation through his own works, and failed miserably. What Jesus accomplished was something so powerful and completely airtight, that no man,woman or principality could break. jesus saved us, a precious gift given again, just like in the beginning when GOD created us and gave us life.