He was killed because He willingly took on the full burden of man. According to Genesis, the burden of man following Adam’s fall was to work the unwilling land and to one day die. Jesus was both God and man at the same time. This is why He willingly died (God can do anything He wants and is not limited to the things our finite minds are limited to). Jesus prayed because He is man and to set an example to man as to how to pray. The reason He did not know the hour is because, again, He was man. Jesus was born a baby and had to learn how to walk and talk and work.