John 15: 1-8, The True Vine

Jesus has been telling the disciples that he is going away, but that they are not to be concerned, for he will leave them with The Counselor. Jesus is either still in the Upper Room or walking with them towards Gethsemane.

John 15: 1‑4, The Vine
“I am the true vine, and my Father is the gardener. 
2 He cuts off every branch in me that bears no fruit, while every branch that does bear fruit he prunes so that it will be even more fruitful. 
3 You are already clean because of the word I have spoken to you. 
4 Remain in me, as I also remain in you. No branch can bear fruit by itself; it must remain in the vine. Neither can you bear fruit unless you remain in me.

A straightforward agricultural metaphor makes it clear that seeking to do good, to be productive in God's kingdom requires being part of the plant, directly linked into the flow of the Holy Spirit from God.

NIV footnotes: "he prunes" could also be translated "he cleans".  So the branch that bears some fruit is "cleaned up" to perform even better.  This fits with verse 3, where Jesus assures the disciples that they are already cleaned up. 

Verse 4 is an admonition; the disciples are to keep this metaphor in mind and make sure to stay connected to their source!

John 15: 1‑8, Remain in Me
“I am the vine; you are the branches. If you remain in me and I in you, you will bear much fruit; apart from me you can do nothing. 
6 If you do not remain in me, you are like a branch that is thrown away and withers; such branches are picked up, thrown into the fire and burned. 
7 If you remain in me and my words remain in you, ask whatever you wish, and it will be done for you. 
8 This is to my Father’s glory, that you bear much fruit, showing yourselves to be my disciples.

Jesus is the source of spiritual nutrient.  We grow like a wild vine if we are linked to him and relying on him.  This is necessary for all who consider themselves a Jesus-follower.  If we stay linked to the vine, we begin to "bear fruit", developing in healthy ways into the person God wants us to become.

The last few verses in this paragraph promise success to those attache to the vine, including answers to their requests (as the teachings of Jesus are deeply learned.)