John 15:1-6
1 I am the true vine, and my Father is the husbandman.
2 Every branch in me that beareth not fruit he taketh away: and every branch that beareth fruit, he purgeth it, that it may bring forth more fruit.
3 Now ye are clean through the word which I have spoken unto you.
4 Abide in me, and I in you. As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in me.
5 I am the vine, ye are the branches: He that abideth in me, and I in him, the same bringeth forth much fruit: for without me ye can do nothing.
6 If a man abide not in me, he is cast forth as a branch, and is withered; and men gather them, and cast them into the fire, and they are burned.
The above passage is used to teach that if a Christian doesn't obey Jesus Christ, then they will go to Hell when they die.
Such see the "taking away" of the branch in verse 2, and the mention of the branch being "cast forth", "withering", and being "burned" in verse 6, as describing a believer losing their Salvation, and being "burned" in Hell.
Let's analyze whether that's a reasonable interpretation of this passage.
Since the consequences mentioned in John 15:6 are a result of failing to "abide" in Christ, it's important to establish what "abiding in Christ" means.
From both the immediate context, and later in the Epistle of First John, we see that "abiding in Christ" means to keep His commandments, and walk entirely in the New Man:
John 15:10
10 If ye keep my commandments, ye shall abide in my love; even as I have kept my Father's commandments, and abide in his love.
1 John 3:6
6 Whosoever abideth in him sinneth not: whosoever sinneth hath not seen him, neither known him.
We know that this is talking about walking in the New Man, because, as discussed at length in this article, the New Man that is born again inside of every believer is utterly sinless (1 John 3:9, 5:18), and "whosoever abideth in him sinneth not". Therefore, only a believer walking in the New Man can abide in Christ.
Also, in context, we see that that the "commandment" that Christ specifically had in mind was the command to love our fellow brothers and sisters in Christ:
John 15:12, 17
12 This is my commandment, That ye love one another, as I have loved you.
17 These things I command you, that ye love one another.
Therefore, we can say that the failure to "abide" in Christ, as spoken about in the passage in question, is a failure to keep Christ's commandments. Specifically, this is summarized, as is done elsewhere (Matthew 22:37-40, etc.), as a command to love fellow human beings.
In the passage in question, Christ likens himself to a "vine", and believers to "branches" on that vine. Then, God the Father is like a "husbandman", who will ensure that the vine produces the maximum amount of fruit.
If a branch bears fruit, God will "purge" (prune) it so that it will bring forth even more fruit (John 15:2). This represents God removing distractions or other negative things from a faithful believer's life, in order for them to do even more for God.
If a branch doesn't bear fruit, it is "taken away" from the vine by the Husbandman (John 15:2), and "cast forth" (John 15:6). Then, as with any part of a plant that has been cut off from its root, it will "wither", and its only use is, naturally, to be "burned" by men (John 15:6).
This is the point of contention with this passage, as the "burning" is often asserted to be referring to going to Hell. However, the "burning" in this metaphor cannot possibly be Hell, as we already know that believers "shall never die" (John 11:26, 6:50), "will not perish" (John 3:15-16), and "shall never perish" (John 10:28), in the eternal sense, and there is no indication that the "branches" in the passage could represent anything other than genuine Christians.
Therefore, this "burning" of a withered branch, broken away from the vine by a husbandman, represents the chastening of the Lord on a wayward believer, who is not bearing fruit. Rather than walking in the New Man, they are walking in the flesh, and so naturally, destruction of the flesh, represented here by the "burning" of a dead tree branch, is what follows:
1 Corinthians 5:5
5 To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
As seen above, "the destruction of the flesh", often up to and including physical death - as is seen in 1 Corinthians 11:30-32 - is the fallout when a believer walks in the flesh (Romans 8:13). It is part of the "chastening of the Lord" (Hebrews 12:6) that any unfruitful believer is subject to. Besides this passage in John chapter 15, this temporal judgment is represented by "fire" elsewhere in Scripture as well (1 Corinthians 3:11-15, Hebrews 6:7-8, 10:26-27).
If, on the other hand, we were to believe most commentators, and see the "burning" in the metaphor as "Hell", we must abandon even the slightest idea that Salvation is "not of works, lest any man should boast" (Ephesians 2:8-9). A commandment to love God and others as Christ loved us, is not only a tremendous undertaking, but totally encapsulates every last part of God's Law (Matthew 22:37-40, etc.). Therefore, if doing so were required to avoid going to Hell, we would be saved squarely by keeping the Law - an idea repudiated over and over again in the Word of God (Galatians 2:16, Romans 3:20-22, etc.), as is the subject of this article.
Besides suffering temporal wrath, the believer who fails to abide also stands to be ashamed that they have wasted their lives before the Lord at the Judgment Seat of Christ:
1 John 2:28
28 And now, little children, abide in him; that, when he shall appear, we may have confidence, and not be ashamed before him at his coming.
Once again, eternal condemnation is not at stake here, but rather "confidence" before the Lord when facing the record of the time that He gave us in His "vineyard" (Matthew 21:28).
This passage does not teach that we get to Heaven by living a life pleasing to God, but rather testifies to the truth that in order for a believer to live a victorious life, they must abide in Christ.
If they do so, they will live an abundant, fruitful life, rather than spiritually "withering" away, and being subject to God's temporal wrath.