In the Bible there is three passages where Jesus Christ Himself says that those that are one with God can be removed from what they have found. The first is in John 15, the next two take place in the third chapter of the book of Revelation.
In John 15 it is established that Jesus Himself is the grape vine and so any branch on the vine is a part of Jesus Christ and so it can be said they have been saved. It states that we are to bear fruit. The key elements to bearing fruit is by living our lives as is taught within the Bible, simply letting Jesus Christ into our life, as well as a few other things, but that is the key element.
Those that do not bear fruit are cut from the vine of Jesus Christ by God Himself. This dead branch is then given over to man and then into the fire.
Now when Jesus talks of fire especially in this context He is referring to the pit of fire. The last home of those that have turned their backs upon God.
John 15: 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 examples from Revelation come from the glorified form of Jesus Christ as He tells John to write to certain churches that existed at the time that John wrote the letters and Revelation. In His letter to Sardis Christ makes reference to the Book of Life. Please pay close attention to the wording:
Revelation 3: 5 He that overcometh, the same shall be clothed in white raiment; and I will not blot out his name out of the book of life, but I will confess his name before my Father, and before his angels.
“Blot out” is the word “exaleipho” in the Greek. This defines as: I wipe away, I plaster, wash over; I wipe off, wipe out, obliterate. This clearly implies that it was there.
In both the imagery is clear. Those mentioned ARE a part of Jesus Christ, but for this to happen they have to be saved, for you can only get into heaven if you are “born again” (John 3:3). This will make you a part of the vine and ensure your name is written in the Book of Life.
In the third example it is Christ’s statement to the lukewarm or those that belief that the world is not black and white but grey.
Revelation 3:15 I know thy works, that thou art neither cold nor hot: I would thou wert cold or hot. 16 So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth.
Now again we must reconcile with the understanding that Jesus is talking to those that have asked Jesus Christ into their hearts. Now though they live a life that is not driven by God, Jesus or the Bible, but by what makes them happy. These are those I refer to as the “Sunday Christians.” They go to church on Sunday sing to God and Jesus, praise and pray to them, then the moment they leave church all bets are off. It is dog eat dog and may the best person win. This is the majority of those that profess to be “Christian” today. They are the “lukewarm.” They are an abhorrence to Jesus and sickens Him so much He spits them from His Body. Again we must understand if He can spit them out they have to have been a part of Him in the first place.
This brings me to 2 Peter 2 where how it will be for the end times. This chapter covers a lot and it should be read and re-read till it sinks in. What is to follow is extremely important to read and understand so I will show it in King James and in New Living Translation
2 Peter 2:20 For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning. 21 For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them.
20 And when people escape from the wickedness of the world by knowing our Lord and Savior Jesus Christ and then get tangled up and enslaved by sin again, they are worse off than before. 21 It would be better if they had never known the way to righteousness than to know it and then reject the command they were given to live a holy life.
Now look at John 3:
3 Jesus replied, “I tell you the truth, unless you are born again, you cannot see the Kingdom of God.” 4 “What do you mean?” exclaimed Nicodemus. “How can an old man go back into his mother’s womb and be born again?” 5 Jesus replied, “I assure you, no one can enter the Kingdom of God without being born of water and the Spirit. 6 Humans can reproduce only human life, but the Holy Spirit gives birth to spiritual life. 7 So don’t be surprised when I say, ‘You must be born again.’
When you are truly born again in the Holy Spirit you are saved and one of the Body of Christ. You are listed in the Book of Life. You become a branch upon the vine of Jesus Christ.
But if you are broken off of the vine, and spit out of the Body then your name is no longer in the Book of Life.
Revelation 20:15 And anyone whose name was not found recorded in the Book of Life was thrown into the lake of fire.

I did not say this. These are not me reading things into the Bible that are not there. This is plain language. This is Jesus Christ HIMSELF saying the words. If you deny His words you are denying Him. Any that deny Him, He will deny to His father.
Matthew 10:32 Whosoever therefore shall confess me before men, him will I confess also before my Father which is in heaven. 33 But whosoever shall deny me before men, him will I also deny before my Father which is in heaven.