This question often comes up in discussions among Christians and there is a healthy debate on whether or not it is possible to lose your salvation. The question and the answer are important because they can affect your relationship with God. For example, if someone believes that he can lose his salvation then he might fall into the error of trying to keep his salvation by what he does. This is a serious error (Gal. 3:1-3). On the other hand, if he believed he could not lose his salvation then, he might fall into the error of sinning willfully because he believes it can't be lost no matter how much he sins. This also is very wrong (Rom. 6:1-2,11-12). The proper understanding of salvation is that works play no part in it (Rom. 4:5), that it is a free gift (Rom. 6:23), and that it is received by faith (Eph. 2:8-9). Once we are saved we are to live a holy life (1 Thess. 4:7).
Fortunately whether you believe you can or cannot lose your salvation does not affect your salvation. That is, your salvation is dependent upon accepting Jesus as Savior, trusting in His sin sacrifice, and looking to no one and nothing else. Your salvation isn't dependent upon whether or not you think it is possible to lose your salvation.
The important point is that you have studied the Word of God and are convinced in your own mind of what you believe (Rom. 14:5). You are the one who has to answer to God (Rom. 3:19). You are the one who needs to study to show yourself approved (2 Tim. 2:15).
There are on the surface good verses for both sides of the argument. There are verses that seem to suggest that it is possible to lose your salvation: 2 Pet. 2:1; Gal. 5:4; Heb. 10:26; 6:4_6; Ps. 69:28, and there are also verses that seem to say you cannot lose your salvation: John 10:27_28; Heb. 13:5; Matt. 7:21_23; 1 John 2:19; Rom. 8:38_39. But if there are verses used to support both sides, then is there a contradiction in the Word of God? Of course not. There can be no contradiction in the inspired Word of God, only in our uninspired misunderstanding.
It is my opinion, and I stress opinion, that it is not possible to lose one's salvation. I base this on scriptures that seem to have a more "eternal" perspective on them. For example, on the day of judgment when some seek salvation based upon their works Jesus will say to them, "I never knew you" (Matt. 7:21-23). They were never known, that is, they were never saved although they appeared, from the human perspective, to be saved. Jesus says that His sheep will "never perish but have eternal life" (John 10:28). How can eternal life be eternal if it can be lost particularly when Jesus said that they will never perish. If they will never perish, then they can't lose their salvation. Also, Paul says that nothing will be able to separate us from the love of God (Rom. 8:38-39). I see these "divine perspective" type verses as giving us glimpses into the viewpoint of God. I see the other verses as being stated from a human perspective, that they appeared to be saved and then appeared to lose it (Gal. 5:4; Heb. 6:4-6). However, 1 John 2:19 says in dealing with antichrists, "They went out from us, but they were not really of us; for if they had been of us, they would have remained with us; but they went out, in order that it might be shown that they all are not of us," (NASB). I see this verse saying two things: First, that if it appears that false teachers leave because they are not regenerated to begin with. In other words, if someone had salvation and then lost it, it was because they never were saved in the first place. Second, it says that if someone is saved, they will remain in the faith.
Nevertheless, there are different positions on this issue. One position states that it is possible to lose your salvation, but only if you want to. In other words, having been set free from sin, the person is then able by an act of will to deny the Lord and desire not to be a part of Him any longer.
Another position states that it is possible to lose your salvation if you sin too much. Then you need to go and confess your sin and get saved again. This has obvious problems because it could lead to someone trusting in his works and God's grace to be saved.
Another position states that it is not possible at all to lose your salvation, that because Jesus has redeemed you and you are a new creation (2 Cor. 5:17) you cannot, then, turn your back on God. Since attaining salvation did not depend on anything you did, keeping it does not depend on anything you do, then also, losing it can't occur because of anything you do.
Unfortunately, this topic has caused far too much friction in the church today. My hope is that people who disagree, can learn to live harmoniously with their eyes on Jesus.