(a.k.a. “Perseverance of The Saints” Under Calvinism)
Another enormously popular false teaching today proclaims that once someone has accepted Christ (i.e., is born again), they can never lose their salvation regardless of how one subsequently lives the rest of their life (i.e., once saved, you are always saved to eternal life no matter what). This false teaching is also called “perseverance of the saints” by Calvinists.
This false teaching asserts that the believer in Christ can choose to keep (obey) the commands of Christ or freely ignore them without any peril, and even choose to live a life of reckless abandon and deliberate/wanton sinful behavior, and yet no matter what, eternal salvation is still ensured. And in the extreme, this false teaching declares that even if one were to deny Christ (after they were born again), they are still saved to eternal life! Now that I understand what Scripture actually says for myself (not just blindly believing whatever I heard taught or preached), I see this for the false teaching that it is!
In this false teaching, it is asserted that your final eternal salvation occurred at an instant of time when you first accepted Christ. However, this book has explained to you the difference between initial salvation (forgiveness of sins) and final salvation (eternal life); it is at final salvation when you receive your “crown of life.” I have also explained that salvation (and sanctification) is a process that starts when you are born again but continues throughout the rest of your life. This book has also explained to you the role that obedience, works, and perseverance has in the plan of salvation. Realize that being born again is only the first step (but by far the most important step) on your path to eternal life – which is your ultimate goal and destination.
In the chapter on Persevering in Faith, I showed you that Scripture is adamant and abundantly clear that one must “persevere” in faith until death, with numerous repeated and explicit warnings about “falling away,” going apostate, “backsliding,” “turning back,” quitting (“abandoning”) the faith, and even being “tricked” or “deceived” out of your “crown of life” by the false teachings of man (the “wolves”) – even after you are born again. While it is true that God will never forsake or leave you, Scripture is abundantly clear that you can still choose to leave/quit Him, even after you have been born again – and that some will do just that! It is written:
In order to fall away, one must have first been part of that faith to begin with. So those who claim that this verse indicates that those who fell away were never truly born-again to begin with are therefore using false logic.
Wayne Jackson writes: 
It should be noted that those who proclaim this false teaching often also falsely teach the conditions for how one is to be born again; therefore, this false teaching is almost always accompanied by the “sinner’s prayer” and the “faith alone/only” false teachings – all three of these false teachings usually come together as an Unholy Trinity pack (where there is one false teaching, others are surely lurking nearby).
 Jackson, Wayne. “But Were They Really Saved?” ChristianCourier.com. Access date: February 20, 2021. https://www.christiancourier.com/articles/1275-but-were-they-really-saved
Anderson, R. John. "6.12 Once Saved Always Saved False Teaching." EachDay.org. Access date: September 29, 2022. https://eachday.org:443/part-vi-beware-the-wolves/6-12-once-saved-always-saved/