Isaiah 65:20

Amongst the blessings of the new people of God the chief shall be a miraculous extension of the term of human life. This is the dominant idea down to the end of Isaiah 65:22. The expression of the thought is unaccountably laboured and obscure.

an infant of days must mean one who lives only a few days.

nor an old man … days (cf. Genesis 25:8; Exodus 23:26; Job 5:26), i.e. none shall become prematurely old; each shall attain the allotted measure of life according to the standard which shall then be normal.

for the youth shall die an hundred years old &c. These two cases must be regarded as hypothetical merely. Death at the age of 100 years (if such a thing took place) would be looked on as an untimely death in extreme youth, and as a special mark of the Divine anger on a career of wickedness (Job 15:32; Job 20:5). The possibility of a hardened sinner being actually found in the Messianic community cannot be seriously contemplated (see ch. Isaiah 60:21).

It is evident that the idea of immortal life is unknown to the writer. He looks forward to a restriction of the power of death, but not to its entire cessation. The same idea is probably implied in a prophecy of the early post-exilic period (Zechariah 8:4; see on ch. Isaiah 25:8); and a conception precisely similar is characteristic of the first section of the Book of Enoch. see Charles, Book of Enoch, pp. 26, 55, 98. Comp. En. Isaiah 5:9: "And [the elect] will not be punished all the days of their life, nor will they die of plagues or visitations of wrath, but they will complete the full number of the days of their life, and their lives will grow old in peace, and the years of their joy will be many, in eternal happiness and peace all the days of their life." Cf. also Isaiah 10:17 and Isaiah 25:4-5.