There are two extremes with the issue of losing your salvation. One position is that once one accept Christ, losing his or her salvation is not possible. The other position is that one moves in and out of salvation. I guess that anyone who believes this has to hope and pray that he dies on the right day!
This page shows what Scripture really teaches on this issue.
Nobody Else Can Take Your Salvation From You
And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand. My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand. (John 10:28-29)
In other words, Satan cannot take anybody's salvation away from him, I cannot take it from him, his pastor/priest cannot take it from him, nor anybody else. Therefore, losing your salvation is not possible by anybody else taking it from you.
Can you Walk Out or Jump Out?
Some claim that John 10:28-29 teaches that you cannot leave of your own accord either. However, what is the context of this passage?
Verily, verily, I say unto you, He that entereth not by the door into the sheepfold, but climbeth up some other way, the same is a thief and a robber. (John 10:1)
All that ever came before me are thieves and robbers: but the sheep did not hear them. (John 10:8)
The thief cometh not, but for to steal, and to kill, and to destroy: I am come that they might have life, and that they might have it more abundantly. (John 10:10)
But he that is an hireling, and not the shepherd, whose own the sheep are not, seeth the wolf coming, and leaveth the sheep, and fleeth: and the wolf catcheth them, and scattereth the sheep. (John 10:12)
The context here is clearly of thieves or wolves snatching sheep. Anyone claiming that John 10:28-29 teaches that nobody can walk out or jump out is definitely taking these verses out of context. To determine if one can give up his own salvation, it is necessary to look at other verses.
But Losing Your Salvation Is Possible By Giving It Up
A Delibrate, In Your Face Sin
For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins, But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries. He that despised Moses' law died without mercy under two or three witnesses: Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace? For we know him that hath said, Vengeance belongeth unto me, I will recompense, saith the Lord. And again, The Lord shall judge his people. It is a fearful thing to fall into the hands of the living God. (Hebrews 10:26-31)
Old Testament Passage
And if any soul sin through ignorance, then he shall bring a she goat of the first year for a sin offering. And the priest shall make an atonement for the soul that sinneth ignorantly, when he sinneth by ignorance before the LORD, to make an atonement for him; and it shall be forgiven him. Ye shall have one law for him that sinneth through ignorance, both for him that is born among the children of Israel, and for the stranger that sojourneth among them. But the soul that doeth ought presumptuously, whether he be born in the land, or a stranger, the same reproacheth the LORD; and that soul shall be cut off from among his people. Because he hath despised the word of the LORD, and hath broken his commandment, that soul shall utterly be cut off; his iniquity shall be upon him. (Numbers 15:27-31)
And let us consider one another to provoke unto love and to good works: Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching. (Hebrews 10:24-25)
But call to remembrance the former days, in which, after ye were illuminated, ye endured a great fight of afflictions; Partly, whilst ye were made a gazingstock both by reproaches and afflictions; and partly, whilst ye became companions of them that were so used. For ye had compassion of me in my bonds, and took joyfully the spoiling of your goods, knowing in yourselves that ye have in heaven a better and an enduring substance. Cast not away therefore your confidence, which hath great recompence of reward. (Hebrews 10:32-35)
No Longer Believing in Christ
Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace. (Galatians 5:4)
For if the firstfruit be holy, the lump is also holy: and if the root be holy, so are the branches. And if some of the branches be broken off, and thou, being a wild olive tree, wert graffed in among them, and with them partakest of the root and fatness of the olive tree; Boast not against the branches. But if thou boast, thou bearest not the root, but the root thee. Thou wilt say then, The branches were broken off, that I might be graffed in. Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear: For if God spared not the natural branches, take heed lest he also spare not thee. Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off. And they also, if they abide not still in unbelief, shall be graffed in: for God is able to graff them in again. For if thou wert cut out of the olive tree which is wild by nature, and wert graffed contrary to nature into a good olive tree: how much more shall these, which be the natural branches, be graffed into their own olive tree? (Romans 11:16-24)
Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him, That ye be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand. Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition; Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God. (2 Thessalonians 2:1-4)
No one you should deceive in not one way, because [it is] if not [until] shall have come the apostasy first, and shall have revealed the man -- of lawlessness, the son -- of destruction,
μή τις μᾶς ἐξαπατήσῃ κατὰ μηδένα τρόπον ὅτι ἐὰν μὴ ἔλθῃ ἡ ἀποστασία πρῶτον καὶ ἀποκαλυφθῇ ὁ ἄνθρωπος τῆς ἁμαρτίας, ὁ υἱὸς τῆς ἀπωλείας
The Greek word ἀποστασία, which appears here in 2 Thessalonians 2:3, literally means defection or revolt. The Merriam-Webster definition of apostasy is: 1) an act of refusing to continue to follow, obey, or recognize a religious faith; or 2) abandonment of a previous loyalty : DEFECTION. The Merriam-Webster definition of apostate is: one who commits apostasy.
The passages Hebrews 10:24-25 and Hebrews 10:32-35 have nothing to do with losing your salvation. I included them since Christians who believe that it is impossible to lose one's salvation claim that people who interpret Hebrews 10:26-31 this way are ripping the passage out of context; and that the passage applies to people who have heard the gospel and rejected it. I have included the verses immediately before and after this passage to show that the passage clearly speaks to Christians. It is ludicrous to believe that Hebrews 10:24-25, which commands church attendance, applies only to people who have heard the gospel and rejected it!
An example of losing your salvation according to the Romans 11:16-24 passage would be that should one convert from Christianity to Islam, God would then judge him as a Muslim; and, like all Muslims, he would end up in hell. This passage also states that, should one convert to Islam, he can convert back to Christianity; God would then judge him as a Christian; and he would end up in heaven.
The passage 2 Thessalonians 2:1-4 clearly shows that there are or will be apostates, those who have abandoned Christianity and have therefore lost their salvation.
Also, since God gave us free will (see my page on free will vs. predestination), we do not lose our free will once we accept Christ and become Christians.
You Do Not Move In and Out of Salvation
And this is the record, that God hath given to us eternal life, and this life is in his Son. He that hath the Son hath life; and he that hath not the Son of God hath not life. These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God. (1 John 5:11-13)
This passage shows that you can know that you have eternal life. If you move in and out of salvation (i.e. you have salvation today, but lose your salvation tomorrow, and have eternal life again the next day), how could you possibly know whether or not you have eternal life?
Many churches that teach this teach either that one is saved by grace + works or that one is saved by grace but kept by works. Works do not enter into whether or not one has eternal life. Please see how to go to heaven for more information.
Therefore, no need to lose any sleep over this!
Salvation Is Not Works Based
A common argument that people who believe that one cannot lose their salvation use is that salvation involves works if one can lose their salvation.
The fact that one can lose their salvation does not mean that salvation is by works, nor that you are saved by faith and kept by works.
For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast. (Ephesians 2:8-9)
But after that the kindness and love of God our Saviour toward man appeared, Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost; Which he shed on us abundantly through Jesus Christ our Saviour; That being justified by his grace, we should be made heirs according to the hope of eternal life. (Titus 3:4-7)
 All scripture references are from the King James Version unless otherwise noted. Please see my about page for why I chose this translation.