Even Jesus had to pray for things he knew God was going to do – he had total assurance that the Holy Spirit would be sent (and in fact talks about him in the present tense in v17), but he still has to ask the Father.

Prayer is such a mystery, isn’t it? I’m often tempted to think I don’t really need to pray as God’s will will be done anyway – why would the almighty God be swayed by my little prayers? But Jesus wasn’t trying to change God’s mind, just asking for that which was already planned.