You can argue that a person was part of a church and that still made them Christian but it still doesn't conform to what the Bible teaches as the "new birth". To be born again. It's been said, "You had nothing to do with your first birth and you have even less to do with your second birth". All of that is up to God. In John Chapt. 3, The Lord Jesus speaking to Nicodemus tells him he needs to be born again of the Spirit of God. And He explains that The Spirit of God is like the wind - it comes and goes, and no one knows whether it's coming or going... it does what it wants a NO ONE controls the wind. Likewise with The Holy Spirit. So it is with the Person who has been indwelt with The Spirit and has been born again. For those who do have an orthodox understanding and still apostatize, it's because the price to align oneself with The One who continues to be hated by the world is indeed too costly. And yes, the Word of God calls us to "count the cost" to follow Him.
