The Cup

Before Jesus went to the cross, he spent the night in the garden of Gethsemane praying, "My Father, if it be possible, let this cup pass from me". He asked for this three times and Luke records that in his anguish his sweat became like drops of blood. What was in this cup that caused this reaction from Christ? Was it merely the fear of physical pain and torment he was about to face, or something much more?