Jesus knew the scriptures so He knew what to expect. However as the hour approached He felt the weight of condemnation beginning to settle in on His soul.

It is that weight from the cup of our sins which would separate Him from the Father, the HolySpirit. He did not want to experience that separation. But since it was necessary He received the cup and drank of it. Rev 14:10 Psm 75:8 Isa 51:17,22 Jer 25:15,17