If it be possible, let this cup pass from me

Matthew 26:39(KJV)
 And he went a little farther, and fell on his face, and prayed, saying, O my Father, if it be possible, let this cup pass from me: nevertheless not as I will, but as thou wilt.

Question: Why would Jesus pray this prayer knowing that it would not change anything?

~ God is able to change his mind and has done so because of prayer
         Ex 32:11-14
        
~ Our persistence in prayer can changes outcomes
          Luke 18:1-8/Luke 11:5-10

~ God wants to give us good things
          Mt 7:7-11/James 1:17

We also have to remember the end of the verse "not as I will, but as thou wilt." - Our will may not be Gods will - we ultimately want what God wants for us :)

 Keep on praying~ Prayer DOES change things! :)