This passage is clear and to the point, but false teachers have twisted these Scriptures and denied their clarity in an attempt to preserve, if possible, the heresy of eternal security. One glaring example of this is Bruce Wilkinson. (Click that link for the details.)
I am the true vine, and my Father is the gardener. 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. (John 15:1,2)
NOTE: Jesus said the fruitless branches were in me. There is no question, Jesus is speaking about real spiritually alive followers, who get their life from the vine. Without doubt, they were saved at one point. This should end the once saved always saved slogan in His grip, referring to an unconditional security and being safe in sin, fruitlessness, etc. Clearly, that is not an accurate understanding of the Heavenly Father. The fruitless are in God's pruning shears, not in his grip and protected.
Jesus is clearly speaking to those who had been forgiven (spiritually cleansed). It is the same ones who got this life or death warning about bearing fruit. The forgiven are the branches, who are in the true vine -- Jesus. The word of God brought their spiritual cleansing. We are born again through the word of God. Peter wrote:
You are already clean because of the word I have spoken to you. (John 15:3)
For you have been born again, not of perishable seed, but of imperishable, through the living and enduring word of God. (1 Pet 1:23)
God's word is imperishable, living and enduring. It must go forth for others to get born again.
God's sovereign will is for all the branches to remain in the vine, but the same God will also cut those same branches off if, through their own negligence, they become unfruitful. It is also assumed those branches had the potential of bearing fruit. If we remain in the vine, the vine will remain in us. It is up to us to remain in him and for our benefit to obey this command to remain. A Christian must remain in Christ, the true vine, to be fruitful -- the only source of spiritual life.
Remain in me, and I will 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. (John 15:4)
Again, Jesus mentions his relationship to his followers is as a vine to branches which can be pruned off and terminated. For the branches to get pruned by the gardener will enable them to bear more fruit. In other words, if a branch survives the gardener's inspection and doesn't get cut off, but just pruned, it will be more fruitful. If a pruned branch could speak, certainly it would say the pruning was painful. Perhaps, some of the painful things that occur to fruitful Christians are part of God's pruning process.
I am the vine; you are the branches. IF a man remains in me and I in him, he will bear much fruit; apart from me you can do nothing. (John 15:5)
Jesus is clearly speaking about those who get cut off by the Father and therefore don't remain or continue in Christ -- the Christians
If anyone does not remain in me, he is like a branch that is thrown away and withers; such branches are picked up, thrown into the fire and burned. (John 15:6)
The cut off branches withered after being severed from the vine, just like what we would observe in the natural. See also Lk. 8:6. For a branch to wither (or die) shows it had life in it before then or it would be impossible for it to wither. Things that have always been dead and lifeless, such as a rock, cannot wither, as those branches did.
The fruitful branches are sustained by their connection to the vine, while the cut off branches (Christians who lost their salvation over fruitlessness) died spiritually and got thrown into the fire. Remember, it is fruit or fire. Their destiny is much different from the branches who remain in and with the vine. The branches remaining in the vine continue to live because of the vine. This is just like:
He who has the Son has life; he who does not have the Son of God does not have life. (1 John 5:12)
See that what you have heard from the beginning remains in you. If it does, you also will remain in the Son and in the Father. And this is what he promised us--even eternal life. (1 John 2:24,25)Jesus is eternal life. It is impossible to have eternal life if we are don't have Jesus.
Verse 7 is a special prayer promise for the fruitful Christians -- the ones who don't get cut off. Such are commanded to ask (God) and it will be given to them. (A fruitful Christian who has God's word remaining in him is not going to ask for things outside God's will.)
If you remain in me and my words remain in you, ask whatever you wish, and it will be given you. (John 15:7)
The Father (gardener) is glorified by fruitfulness. That is also how one can be recognized as a disciple of Christ. This alone destroys the teaching of once saved always saved. Heretic Charles Stanley teaches the opposite of the Lord Jesus:
This is to my Father's glory, that you bear much fruit, showing yourselves to be my disciples. (John 15:8)
... a Christian who at no point in his entire life bore any eternal fruit. And yet his salvation is never jeopardized (Eternal Security: Can You Be Sure, p.121).