'''Eternal security''' is the doctrine of unconditional '''eternal salvation''' as an irrevocable gift of salvation from [[God]] through [[Jesus Christ|Christ]] as Savior. 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].
[[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:*[http://www.justforcatholics.org/a161.htm Was Luther an Antinomian? (justforcatholics.org)] ''A sympathetic assessment of Luther' Letter to Melancthon by a Roman Catholic [[Apologetics|apologist]].''*[http://www.scrollpublishing.com/store/Luther-Sin-Boldly.html Online text of Martin Luther's Letter to Phillip Melancthon Sin Boldly (scollpublishing.com)]</ref>
There are those who reject this doctrine as a [[heresy]]<ref>Primarily the [[Catholic Church]] and the [[Orthodox Church]]</ref> on the basis of [https://www.biblegateway.com/passage/?search=Hebrews+6%3A4-8&version=KJV Hebrews 6:4-8]; [https://www.biblegateway.com/passage/?search=2+Peter+2%3A18-22&version=KJV 2 Peter 2:18-22]; [https://www.biblegateway.com/passage/?search=Jude+1%3A3-4&version=KJV Jude 3-4], [https://www.biblegateway.com/passage/?search=Jude+1%3A8&version=KJV 8], [https://www.biblegateway.com/passage/?search=Jude+1%3A12-13&version=KJV 12-13], [https://www.biblegateway.com/passage/?search=Jude+1%3A16-19&version=KJV 16-19] <ref>Jude 16-19 was seen as especially applicable to Martin Luther because of his [[polemic]] against the hierarchy of the Catholic Church and his doctrine of Christian freedom and unconditional salvation; see his pamphlet [http://www.lutherdansk.dk/Web-babylonian%20Captivitate/Martin%20Luther.htm ''On the Babylonian Captivity of the Church''] and the Catholic document of Pope Leo X, the papal bull [http://www.papalencyclicals.net/Leo10/l10exdom.htm ''Exsurge Domini'' Condemning the Errors of Martin Luther].</ref>; and [https://www.biblegateway.com/passage/?search=Matthew+7%3A21-23&version=KJV Matthew 7:21-23]; [https://www.biblegateway.com/passage/?search=Matthew+25%3A14-46&version=KJV 25:14-46]—also [https://www.biblegateway.com/passage/?search=James+2%3A14-26&version=KJV James 2:14-26] and [https://www.biblegateway.com/passage/?search=1+John+3%3A17-18&version=KJV 1 John 3:17-18]; compare [https://www.biblegateway.com/passage/?search=Romans+8%3A1&version=KJV Romans 8:1] with [https://www.biblegateway.com/passage/?search=1+John+3%3A7-8&version=KJV 1 John 3:7-8]. See [https://www.biblegateway.com/passage/?search=Luke+13%3A6-9&version=KJV Luke 13:6-9]; [https://www.biblegateway.com/passage/?search=Luke+19%3A12-26&version=KJV 19:12-26].