Charles Ellicott Commentary Isaiah 38:21

"Now Isaiah had said, Let them take a cake of figs, and lay it for a plaster upon the boil, and he shall recover." — Isaiah 38:21 (ASV)

For Isaiah had said ... —The direction implies some medical training on the part of Isaiah (see Note on Isaiah 1:6, and Introduction), such as entered naturally into the education of the prophet-priests. They were to Israel, especially in the case of leprosy and other related diseases, what the priests of Asclepios were to Greece. The Divine promise guaranteed success for the use of natural remedies but did not dispense with them. These remedies, like the spittle laid on the eyes of the blind in the Gospel miracles (Mark 7:33, John 9:6), also served as an aid to the faith on which the miracle depended.

Both this and the following verse seem, as has been said, to have been notes to Isaiah 38:8, supplied from the narrative of 2 Kings 20:0, and placed at the end of the chapter instead of at the foot of the page, as in modern manuscripts or print. The word for “boil” appears in connection with leprosy in Exodus 9:9, Leviticus 13:18, but is used generically for any kind of abscess, carbuncle, and the like .