James 5:19-20

¹⁹ Brethren, if anyone among you wanders from the truth, and someone turns him back,

²⁰ let him know that he who turns a sinner from the error of his way will save a soul from death and cover a multitude of sins.

a soul (v.20) = the turned back sinner

multitude of sins (v.20) — 1 Peter 4:8

It is noteworthy that James is addressing the “brethren” as he closes the epistle. If any one among them, who knew the Lord, departed from the truth, the one who restores him to the faith was to be commended. In this context, the truth is the kingdom gospel. Whenever some of their number wandered from the teachings of the Sermon on the Mount every effort was to be made to restore them to the faith. Solomon calls the soul that leaves his spiritual moorings a blackslider, whose heart is “filled with his own ways” (Proverbs 14:14). 

The statement “and one converteth him,” has the idea to encourage the fallen believer to turn from the error of his way. In so doing, the one who has invested the time to minister to this wayward soul may well have saved him from death, that is, physical death. In biblical times, the judgment of God upon sin was often swift and sure, especially at the beginning of a new dispensation (1 Corinthians 5:1-5; 11:29; 1 John 5:16). God was teaching them, of course, that sin had serious consequences. When a brother in Christ repented, it covered a multitude of sins, not only because he would be forgiven for confessing his sins, but also because he was restored to fellowship with God, which meant he wouldn’t slip deeper into sin (1 John 1:7-9). — Sadler, pages 141-142.