"But in your hearts set apart Christ as Lord. Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, keeping a clear conscience, so that those who speak maliciously against your good behavior in Christ may be ashamed of their slander." ~ 1 Peter 3:15-16
Eternal Security - Can a Christian lose his salvation?

I think, first and foremost, salvation is by grace alone. So if we are secured in His grace, there's really no issue to whether believers would lose their salvation, unless God Himself choose to withdraw His grace from us, and in that case we will all be hopelessly dead. Therefore if it is by grace alone, then work will have no part in it, and it is a misleading question to ask if one can lose his salvation because of what he did. In my opinion, it's like a murderer doubting if he could be saved because of what he did in the past. And for those who think that we can work our way up, I put this forth to you. Do you know how much work is considered enough and have you done enough? In fact, if we do think that our work is going to have a say in our salvation, then it renders the Cross totally meaningless. What does Christ's death on that Cross means, if we cannot trust in His work, grace and love, but have to rely on our own human endeavour? Are we now saying that Christ's death has its limits?

Indeed, salvation is by grace alone, and it is not automatically make available to all but faith is required. Therefore, the only "work" on our part is to stand firm in the faith. The only case of losing one's salvation, it seems to be, would be disbelief, the case of losing one's faith by which the christian life is first started out with. Amazingly, the Holy Spirit is here to help us, even our doubts. So again, it is not I who work my way up, but He who works in me from within out, by His grace alone. In fact, Eph 1:13 told us that the depositing of the Holy Spirit as the seal of promise in us, is the evidence of our salvation. The only case of losing our own salvation is to, by our choice, reject the Holy Spirit/God who could save us. It is as if to reject the only plank of wood which could save one from drowning.