A.T. Robertson Commentary James 5:20

"let him know, that he who converteth a sinner from the error of his way shall save a soul from death, and shall cover a multitude of sins." — James 5:20 (ASV)

Let him know (γινωσκετω). Present active imperative third person singular of γινωσκω, but Westcott and Hort read γινωσκετε (know ye) after B. In either case it is the conclusion of the condition in verse 19.

He which converteth (ο επιστρεψας). First aorist active articular participle of επιστρεφω of verse 19.

From the error (εκ πλανης). "Out of the wandering" of verse 19 (πλανη, from which πλαναω is made). See 1 John 4:6 for contrast between "truth" and "error."

A soul from death (ψυχην εκ θανατου). The soul of the sinner (αμαρτωλον) won back to Christ, not the soul of the man winning him. A few MSS. have αυτου added (his soul), which leaves it ambiguous, but αυτου is not genuine. It is ultimate and final salvation here meant by the future (σωσε).

Shall cover a multitude of sins (καλυψε πληθος αμαρτιων). Future active of καλυπτω, old verb, to hide, to veil. But whose sins (those of the converter or the converted)? The Roman Catholics (also Mayor and Ropes) take it of the sins of the converter, who thus saves himself by saving others. The language here will allow that, but not New Testament teaching in general. It is apparently a proverbial saying which Resch considers one of the unwritten sayings of Christ (Clem. Al. Paed. iii. 12). It occurs also in 1 Peter 4:8, where it clearly means the sins of others covered by love as a veil thrown over them. The saying appears also in Pr 10:12 "Hatred stirs up strife, but love hides all transgressions"--that is "love refuses to see faults" (Mayor admits). That is undoubtedly the meaning in 1 Peter 4:8; James 5:20.