Jamieson, Fausset and Brown on James 5:15

15. prayer--He does not say the oil shall save: it is but the symbol.

save--plainly not as Rome says, "save" the soul. but heal "the sick": as the words, "the Lord shall raise him up," prove. So the same Greek is translated, "made (thee) whole," Mt 9:21, 22.

and if ... sins--for not all who are sick are so because of some special sins. Here a case is supposed of one visited with sickness for special sins.

have committed--literally, "be in a state of having committed sins," that is, be under the consequences of sins committed.

they--rather, "it": his having committed sins shall be forgiven him. The connection of sin and sickness is implied in Is 33:24; Mt 9:2-5; Joh 5:14. The absolution of the sick, retained in the Church of England, refers to the sins which the sick man confesses (Jas 5:16) and repents of, whereby outward scandal has been given to the Church and the cause of religion; not to sins in their relation to God, the only Judge.