A: Let me start by saying that I very much dislike this question. Very few people ask this question because of a genuine desire to learn. I find that most Christians have their minds pretty well made up on the subject and they ask this question so they might know if I've embraced the correct side.
By "sides" I'm referring to the two very opposed schools of thought on this question. The first is Armenianism and in its extreme form it teaches that the security of your salvation is thrown away each and every time you sin, and only after confessing and repenting of that sin is your salvation restored.
The other position is called Calvinism which is a part of Reformed Theology, and it holds that once a person is saved it's impossible for them to ever lose that salvation for any reason. If anyone claims to be a believer and walks away from the Lord, a Calvinist explains it all by saying that person was never a believer in the first place.
I have a problem with both Armenianism and Calvinism. And the reason is because I find the New Testament filled with repeated warnings written to born-again believers about the danger of abandoning faith and walking away from Christ. (And by walking away from Christ, I am not talking about committing a sin. Believers cannot lose their salvation by sinning any more than they can earn it by doing good.)
If walking away from the Lord in unbelief isn't possible as the Calvinist teaches, I have to ask myself why there are so many warnings like the ones below scattered throughout the New Testament. Warnings like:
1 Corinthians 15:1-2 (ESV)
Now I would remind you, brothers, of the gospel I preached to you, which you received, in which you stand, and by which you are being saved, if you hold fast to the word I preached to you—unless you believed in vain.
The Apostle Paul believed that it was possible to "believe in vain."
Look: I, Paul, say to you that if you accept circumcision, Christ will be of no advantage to you. I testify again to every man who accepts circumcision that he is obligated to keep the whole law. You are severed from Christ, you who would be justified by the law; you have fallen away from grace.
The Apostle Paul believed that it was possible to "fall away from grace."
Hebrews 2:1-3a (ESV)
Therefore we must pay much closer attention to what we have heard, lest we drift away from it. For since the message declared by angels proved to be reliable, and every transgression or disobedience received a just retribution, how shall we escape if we neglect such a great salvation?
The author of Hebrews believed it was possible to "drift away" from the message of faith in Jesus Christ.
I understand there are many sincere followers of Christ who passionately reject any idea of a true believer walking away from the Lord in unbelief. I respect their position, but as I study the Word of God, I cannot embrace it because of these repeated warnings by New Testament authors about doing that very thing. As a Bible teacher, I feel it is my responsibility to respectfully communicate the message of God's Word without bias or partiality. Although it seems impossible to imagine someone being saved and later being unsaved, each and every believer must ultimately allow the Word to be the final word concerning what they believe about this issue.