My concern is not with whether or not a person believes they have accepted Jesus Christ as Lord and Savior by grace through faith, but the words used to be a Christian.
What I mean is that biblically speaking, if a person does repent of sin and by faith accepts Christ as Savior; they are in fact saved at that very moment and become what is known as a Christian. As a Christian we are to following the Word of God (Bible) as our authority, even if it means going against the traditions of men that also claim to be Christians.
Baptist, which I am, believe we are saved by faith alone, we are baptized in obedience (without it effecting our salvation one bit), and that tongues are not for today, which most fail to follow 1 Corinthians 14 anyway.
When one says that they used to be a Christian, they are immediately placed into one of two categories:
1] They actually did receive Christ as Savior one day and have currently decided to turn their backs on all that they know to be true, yet are still saved.
2] They never actually received Christ as Savior and are currently still unsaved.
At the very point of salvation (this is where one has to know their own experience with Christ) - without tongues or baptism - they are sealed by the Holy Spirit [Ephesians 1:13; Ephesians 4:30], they are kept by the power of God [1 Peter 1:5], cannot be separated from the love of Christ [Romans 8:33-39]. Therefore, salvation cannot be lost.
So being a Christian is because of the new birth by Christ. All the things that follow like going to church, etc. come from the new birth because one is now a Christian, they do not make one a Christian - Christ did.
Therefore if you truly accepted Jesus Christ when you say you did, then you are still a Christian today - not because you choose not to do the things the Bible says, but because Christ saved you the day you called on Him. On the other hand if you did not really accept Christ that day (and only you know) then you never were a Christian and aren't one today.
I hope this clears up what I mean, even if you disagree. Here is a verse to ponder.
2 Timothy 2:13, If we believe not, yet he abideth faithful: he cannot deny himself.