It's a bit complex, but I think you know the story. Jesus (the man) literally sweated blood the night He prayed in the garden Gethsemane because being omniscient, He knew what He as in for commencing in just a few hours and over the next day. He concluded His prayer session with words to the effect,"Father, Your will be done." I think you know that Christians believe that Jesus was fully human and at the same time fully divine. He was and is His Father in Heaven while at the same time He was and is the so-called 'Son'. He knew and understood His self-appointed mission to sacrifice Himself in the place of sinful mankind. (You know your John 3:16 too, right?) God, The Father, chose to call his human incarnation (his avatar - this is the original meaning of the word - a human incarnation of a god) His 'Son' not because Jesus was His Son in the literal, human sense of the word, but because He wanted us to understand the close and loving relationship between that Man Jesus and Himself - how much Jesus meant to Him... So yes, He freely made the sacrifice, but as a human being just like you or me, He could not help being terribly frightened. To his day has anyone dies a more horrific death? I refer you also to John 15:13 - such was Jesus' selflessness. You also will recall that when the soldiers came to arrest Him, and they asked if he were Jesus of Nazareth, He answered, "I am he." and bowled them right over (twice). He could have easily escaped as He had escaped angry mobs many times in the past, but this was His self-appointed hour to redeem humanity.