James 5:19-20- Brethren, if any of you do err from the truth, and one CONVERT him; let him know that he which CONVERTETH the sinner from the error of his way, shall SAVE A SOUL FROM DEATH, and shall hide a multitude of sins.
This passage is such a difficulty for eternal security adherents that many dismiss the book of James as not being applicable to the New Testament believer.
Their argument is it was written to the Jews not them.
Anyway this clearly shows the BROTHER who DEPARTS from the TRUTH (Jesus John 14:6) must be converted back (born again again?) or he will experience eternal death (Romans 6:23).
Previously converted (any of you), departed, needed to be converted back again and now referred to as a sinner (1 Peter4:18, John 9:31) which is the opposite of what believers are referred to (righteous Peter 4:18, 2 Corinthians 5:21, 1 John 3:7, 1 John 2:29).