And in that day ye shall ask Me nothing. Verily, verily, I say unto you, Whatsoever ye shall ask the Father in My Name, He will give it you.
Hitherto have ye asked nothing in My Name: ask, and ye shall receive, that your joy may be full.
In that day would seem, in the context, to refer to His resurrection, when many of the disciples’ questions would finally be answered and their joy would be full in the knowledge of His victory over sin and death. Jesus was saying that they would have no more questions for Him at that time, in their great joy at seeing Him alive.
Then, Jesus went on to teach them that now they could go directly to the Father with their needs, wants, and desires. Since He was the Great High Priest, they could ask the Father anything in the Name of Jesus.
This concept was new for the disciples. Their custom, all their lives, had been to come to the High Priest to offer their sacrifices; they went to God through the human offices of the priests. Now, they didn’t have to do so ever again. They had direct access to the Father through the Son, which is why so many of us today pray “in Jesus’ Name.”
The coming of the Holy Spirit would help them understand their new access to the Father through the Son. The Spirit would teach them how to pray, with Jesus as the Mediator between God and Man, with no human mediator needed.
Until that point, the disciples had asked nothing of the Father in Jesus’ Name. Now, He encouraged them to ask in His Name, and promised that they would receive answers to their prayers, and that they would have great joy in doing so.
John 17, the next chapter, will teach us a great deal about real prayer–truly, the Lord’s Prayer, in a completely different sense than the “Our Father” pattern that Jesus had offered them earlier.