I don't like this question.
If I think the person asking just enjoys arguing over Scripture then I answer: "From a purely practical standpoint, if a man is not saved does it really matter whether he had his salvation and then lost it or whether he never had it in the first place? It's not my job to figure out how he got into the mess he's in; it's my job to help him get right with God so God can help him out."
Otherwise, I usually answer this question with another question, "Why do you want to know?" because the reasons for asking differ:
- Some people are concerned about another person's salvation. They have a child, parent, or other loved who at one time or another appeared to be right with God, but no longer act like it.
- Some people are insecure about their own salvation. They thought they gave their heart to Jesus, but no longer "feel" like it because of the way they often behave.
- Some people want to justify their current lifestyle. They "live like hell" in this life but don't want to spend eternity there.
If you have any of the above reasons for asking the question, please search through the Categories for "salvation" where I go into a more useful discussion.
God has nothing to do with this question. God is not fickle and He does not change (Hebrews 13:8). He's not trying to keep people out of Heaven; He wants everybody with Him (John 3:16-17, John 12:32). Unfortunately, not everyone is with Him. But it's not God who does the leaving-it's us (Hebrews 13:5). What's amazing is that even when we leave Him He is close by (Psalm 139:7-12).
Many people consider themselves to be right with God because of membership in a church, or because they agree with the Christian Religion, or because they consider themselves to be good persons. I can see how this question could and should come up in these circles. And maybe with enough arguing a few will see that salvation has nothing to do with them and everything to do with Jesus.
But if you're not in one of these groups, I encourage you to study John, 1 John, 2 John, and 3 John. As you study I believe you will lose interest in the question.