It requires the physical & emotional pain to fulfill the will of God the Father,

The physical;as the Holy scripture say without the Shedding of the Blood there is no Forgiveness of sin.

During the Last Supper with his 12 disciples (Mat.26 :26-28 ) Jesus Christ as he took the bread and before he give the bread to his disciples,he blessed it and said this is my "body " and same he did on the cup and he said into the cup this is my blood of the new and everlasting covenant which will be shed for all men for the forgiveness of sin.

The emotional pain I think,is when Jesus Christ prayed in the Gardens of gethsemane where this scene demonstrate that Jesus Christ feel(emotion)the pain of being departed from his disciples

In the Book of Matthew it has been three times that Jesus Christ told about the sufferrings,his crucifixion on the cross, and the ressurection that is going to happen and shall be witness both the Jews and the believers.While he was telling these to his disciples,they could not bear the things he was telling;In Matthew 16:21-23 Apostle Peter try to rebuke Jesus Christ,this must not happen to him (Jesus Christ ) Jesus told Peter  "Get away from me Satan"

He foretold the things to hapen to his disciples for them to know that when it come to pass they will remember that it has been told.