Is the doctrine of once saved, forever saved true?  Are those who “fall away” not the true disciples from the beginning?

Once saved, always saved, also known as “perseverance of the saints,” is a false doctrine that was created in the sixteenth century by the likes of Ulrich Zwingli and John Calvin and is part of classical Calvinism.  This doctrine is not taught in the Bible.  You noticed that belief in this false doctrine forces us to the ad hoc conclusion that if someone appears to have fallen away, then they were never saved in the first place.  This is like a kind of logical gymnastics which is forced on the purveyors of the idea of once saved, always saved.  I suggest you read the Book of Hebrews and ask what it teaches about losing our salvation.  The principal purpose of the Book of Hebrews is to prevent saved people from losing their salvation.  I have published a book on Hebrews Hebrews: Living by Faith.   It is available at www.ipibooks.com.   I have not supplied the relevant scriptures in this too-brief answer, but that is because I have produced an outline that goes into a fair amount of detail on this false doctrine.  Once Saved Always Saved  There are plenty of scriptures in this outline to explain the history of the false doctrine and provide scriptural support for the conclusion that one can lose one’s salvation.  I hope this helps.

John Oakes