Job 18:13

It shall devour the strength of his skin - Margin, bars. The margin is a correct translation of the Hebrew. The word used (בדי badēy, construct with עורו ‛ôrô - his skin) means bars, staves, branches, and here denotes his limbs, members; or, more literally, the bones, as supports of the skin, or the human frame. The bones are regarded as the bars, or the framework, holding the other parts of the body in their place, and over which the skin is stretched. The word “it” here refers to the “first-born of death” in the other hemistich of the verse; and the meaning is, that the strength of his body shal be entirely exhausted.

The first-born of death - The “first-born” is usually spoken of as distinguished for vigor and strength; Genesis 49:3, “Reuben, thou art my first-born, my might, and the beginning of my strength;” and the idea conveyed here by the “first-born of death” is the most fearful and destructive disease that death has ever engendered; compare Milton’s description of the progeny of sin, in Paradise Los. Diseases are called “the sons or children of death” by the Arabs, (see Schultens in loc.,) as being begotten by it.