Jesus' death on the cross has been called a "substitutionary" death, in other words a death in the place of us.  Our own sin has separated us from God and it is us that really deserve to die.  For Jesus' death to truly be a substitute for a death that we deserve, Jesus had to die a fully human death, in body, soul and spirit.  This involved physical and emotional pain just as well as spiritual separation.  That fact that Jesus faced this without sin qualified him to be the once for all sacrifice for sin that sets us free from sin!  What amazing love, that God would not spare his own Son but deliver Him up for us all!