The spirit of slumber. — This phrase, again, has a curious history. Etymologically, the word translated “slumber” would seem to agree better with the marginal rendering, “remorse.” It comes from a root meaning to “prick or cut with a sharp instrument.” There happens to be another root somewhat similar, but certainly not connected, which means “drowsiness,” “slumber.” Hence, where the word in the text has been used to render the Hebrew word for “slumber,” it has been thought that there was a confusion between the two. It appears, however, from the LXX. usage, that the sense of “slumber” had certainly come to attach to the word here used by St. Paul. From the notion of a sharp wound or blow came to be derived that of the bewilderment or stupefaction consequent upon such a blow, and hence it came to signify stupor in general.
The quotation is a free combination of two passages of the LXX. (Isaiah 29:10, and Deuteronomy 29:4), no doubt put together by the Apostle from memory.