Jesus the Messiah put Himself through the process of physically dying (in agony) to show the world that He understands the sad plight of humanity in His wonderful creation though suffering under the curse by the sin committed by Adam and Eve almost six thousand years ago (their fall was perhaps thirty years after the six days of creation), so when children ask why He had to die on the cross, tell them it was to reverse the curse, manifested in the born again and the fully redeemed creation in the future.
