“You did not choose me, but I chose you and appointed you to go and bear fruit—fruit that will last. Then the Father will give you whatever you ask in my name.” (John 15: 16)
In another hard saying of Jesus (as quoted above), Jesus told the apostles when they understood that He chose them to be fruitful God would answer their prayers! Jesus told them they did not choose Him to be part of their plans. He chose them to be part of His plans and when they got that God would answer their prayers.
The three years Jesus had been with them were like a seminary. These four chapters (13-16), of the Gospel of John record His commencement address to them. In Chapter 15 He gave them at least six reasons why they must be fruitful. Those reasons were:
They must be fruitful because there is no such thing as a disciple of His who is not fruitful. This is how they show they are His disciples. They must be fruitful because this is how they glorify God. They must be fruitful that their joy might be full. They must be fruitful because He chose them to be fruitful. Finally, they must be fruitful because He is the Vine and they are the branches. That is, He has no other way to accomplish His work in this world.
In His metaphor about the Vine and the branches the fruit does not grow on the Vine. This means the risen Christ has limited Himself to faithful branches. Although we may not have done it that way it is the plan of the risen Christ to use His power in His disciples to accomplish His work and speak His word in this world.