Then let mine arm - The strong language which Job uses here, shows his consciousness of innocence, and his detestation of the offences to which he here refers, Job 31:16-22. The word rendered “arm” here (כתף kâthêph) means properly the shoulder. Isaiah 46:7; Isaiah 49:22; Numbers 7:9; compare the notes at Isaiah 11:14. There is no instance, it is believed, unless this is one, in which it means arm, and the meaning here is, that he wished, if he had been guilty, his shoulder might separate from the blade. So Herder, Rosenmuller, Umbreit, and Noyes render it; and so the Vulgate and the Septuagint.
From my shoulder-blade - The scapula - the flat bone to which the upper arm is attached. The wish of Job is, that the shoulder might separate from that, and of course the arm would be useless. Such a strong imprecation implies a firm consciousness of innocence.
And mine arm - The word arm here denotes the forearm - the arm from the elbow to the fingers.
From the bone - Margin, “the chanelbone.” Literally, “from the reed” - מקנה miqâneh. Umbreit renders it, Schneller als ein Rohr - quicker than a reed. The word קנה qâneh means properly a reed, cane, calamus (see the notes at Isaiah 43:24), and is here applied to the upper arm, or arm above the elbow, from its resemblance to a reed or cane. It is applied, also, to the arm or branch of a chandelier, or candlestick, Exodus 25:31, and to the rod or beam of a balance, Isa. xlvi. 6. The meaning here is, that he wished that his arm should be broken at the elbow, or the forearm be separated from the upper arm, if he were guilty of the sins which he had specified. There is allusion, probably, and there is great force and propriety in the allusion, to what he had said in Job 31:2 l: “If his arm had been lifted up against an orphan, he prayed that it might fall powerless.”