It is also called, "'''Once saved, always saved'''", a nickname for the belief that we are eternally saved from [[sin]] and damnation to [[hell]] once and for all eternally by faith alone, ''[[sola fide]]'', by believing in Jesus Christ as one's own personal Savior, without any merit or any earning of [[salvation]] by anything the repentant sinner can do, and that once it has been given and received by accepting Christ "into your heart" as Lord and Savior, salvation and eternal glory in heaven with God cannot ever be lost or forfeited or revoked. See [https://www.biblegateway.com/passage/?search=Romans+8%3A38-39&version=KJV Romans 8:38-39]; [https://www.biblegateway.com/passage/?search=Romans+10%3A10-11&version=KJV 10:10-11].
There are holders of the "once saved" position who argue that merely mouthing the sinner's prayer or similar words makes one guaranteed to go to heaven even if one renounces Christianity and/or engages in grossly immoral lifestyle.
[[Martin Luther]] famously wrote: "Be a sinner, and let your sins be strong (sin boldly), but let your trust in Christ be stronger...No sin can separate us from Him, even if we were to kill or commit adultery thousands of times each day." (Martin Luther: ''Letter to Melanchthon'')<ref>See the following: