Adam Clarkes' comments are worth reading:

Is any sick among you? let him call for the elders - This was also a Jewish maxim.

Rabbi Simeon, in Sepher Hachaiyim, said: “What should a man do who goes to visit the sick? Ans. He who studies to restore the health of the body, should first lay the foundation in the health of the soul. The wise men have said, No healing is equal to that which comes from the word of God and prayer.

Rabbi Phineas, the son of Chamma, hath said, ‘When sickness or disease enters into a man’s family, let him apply to a wise man, who will implore mercy in his behalf.’“ See Schoettgen.

St. James very properly sends all such to the elders of the Church, who had power with God through the great Mediator, that they might pray for them.

Anointing him with oil -

If a miracle was intended, it could have been as well wrought without the oil, as with it.

It is not intimated that even this unction is to save the sick man, but the prayer of faith, James 5:15.

What is here recommended was to be done as a natural means of restoring health, which, while they used prayer and supplication to God, they were not to neglect.

Oil in Judea was celebrated for its sanative qualities; so that they scarcely ever took a journey without carrying oil with them, (see in the case of the Samaritan), with which they anointed their bodies, healed their wounds, bruises, etc.

Oil was and in frequently used in the east as a means of cure in very dangerous diseases; and in Egypt it is often used in the cure of the plague. Even in Europe it has been tried with great success in the cure of dropsy. And pure olive oil is excellent for recent wounds and bruises; and I have seen it tried in this way with the best effects.

But that it was the custom of the Jews to apply it as a means of healing, and that St. James refers to this custom, is not only evident from the case of the wounded man ministered to by the good Samaritan, Luk_10:34, but from the practice of the Jewish rabbins. In Midrash Koheleth, fol. 73, 1, it is said: “Chanina, son of the brother of the Rabbi Joshua, went to visit his uncle at Capernaum; he was taken ill; and Rabbi Joshua went to him and anointed him with oil, and he was restored.” They had, therefore, recourse to this as a natural remedy; and we find that the disciples used it also in this way to heal the sick, not exerting the miraculous power but in cases where natural means were ineffectual. And they cast out many devils, and anointed with oil many that were sick, and healed them; Mar_6:13. On this latter place I have supposed that it might have been done symbolically, in order to prepare the way for a miraculous cure: this is the opinion of many commentators; but I am led, on more mature consideration, to doubt its propriety, yet dare not decide. In short, anointing the sick with oil, in order to their recovery, was a constant practice among the Jews. See Lightfoot and Wetstein on Mark 6:13. And here I am satisfied that it has no other meaning than as a natural means of restoring health; and that St. James desires them to use natural means while looking to God for an especial blessing. And no wise man would direct otherwise.

St James orders this anointing for the cure of the body

The anointing with oil, if ever used as a means or symbol in working miraculous cures, was only applied in some cases, perhaps very few, if any...

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Richard
CofE
UK