This verse mixes the two metaphors found in verse 16, namely fire and sickness. Good News Translation brings out the link between the two figures of speech clearly. In Hebrew the second image is in the form of a simile (it will be as when …). Also, the image of destruction in verses 18-19 takes on a very realistic quality, speaking of the devastation of forests and farmland.
The glory of his forest and of his fruitful land the LORD will destroy: Not only will Yahweh burn and destroy Assyria’s weeds and small shrubs (verse 17), but he will also do it to the forests and farmland. Forest and fruitful land includes the entire territory of the nation. The two expressions are not merely two specific kinds of land.
Most translations consider the noun glory to be an adjective describing the forest; for example, “rich forests” (Good News Translation), “splendid forest[s]” (Revised English Bible, New American Bible), and “luxuriant forest” (New Jerusalem Bible). His fruitful land renders a Hebrew noun (karmel) that can refer to very fertile land as in 32.15, or to the (fertile) Carmel region as in 33.9. All versions consulted take it to refer here to fertile farmland. Both The glory of his forest and his fruitful land are placed before the verb in the Hebrew text to draw attention to them. Some languages may prefer to place these phrases after the verb. The subject the LORD is not in the Hebrew text, but Revised Standard Version has added it for clarity. Good News Translation uses the passive verb “be … destroyed” since it does not add this subject. The Hebrew verb translated destroy literally means “bring something to completion.” It strongly hints at the totality of the destruction.
Both soul and body is probably an idiomatic phrase to express completeness, in this case the completeness of the destruction. The Hebrew term translated soul refers to the life force of an individual (see the comments on 1.14). But in the Hebrew text both soul and body is linked closely with the destruction of forests and farmland, and not to the following line that speaks of a sick man. Some think that the phrase is similar in function to the phrase “From the sole of the foot even to the head” in 1.6 or “head and tail” in 9.14. It expresses completeness like the English expression “from top to bottom.” Good News Translation says “totally,” and Bible en français courant has “from bottom to highest top.”
And it will be as when a sick man wastes away: Here the prophet speaks of a sick person gradually growing weak. The Hebrew word rendered wastes away (which can also mean “melts away”) differs from the noun rendered “wasting sickness” in verse 16. Revised English Bible says “as suddenly as someone falling in a fit,” and Die Bibel im heutigen Deutsch has “like someone mortally ill,” but most translations use a verb with the sense of “wasting away.”
Suggested translation models for this verse are:
• Assyria’s luxuriant forests and farmland will be destroyed totally;
it will be like a sick person wasting away to nothing.
• Its wonderful forests and farmlands will be completely destroyed; it will be like someone fading completely away.
Quoted with permission from Ogden, Graham S. and Sterk, Jan. A Handbook on Isaiah. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here .