1 Peter 1:24 is a citation of Isaiah 40:6-8. This passage, within its immediate context is a powerful testimony to the faithfulness of God to Israel because “the word of our God shall stand forever.” The first voice of chapter 40 in found in verse 3 which prophetically speaks of John the Baptist preparing the way for the Messiah, (Matt. 3:3; Luke 3:4). The prophet hears a second voice in verse 6, “The voice said, Cry.” And he said, “What shall I cry?” A third voice heralds the Messiah as their God in verses 9 and following. Within the context of this three-part announcement, the second voice “celebrates the divine word of promise in the face of the approaching fulfillment and appoints a preacher of its eternal duration.” The theme of his message is the perishable nature of all flesh and the imperishable nature of the word of God. Keil and Delitzsch comment,
Men living in the flesh are universally impotent, perishing, limited; God, on the contrary (ch. xxxi. 3), is omnipotent, eternal, all-determining; and like Himself, so is His word, which, regarded as a vehicle and utterance of His willing and thinking, is not something separate from Himself, and therefore is the same as He.
Verse 7a describes what happens to the grass and the flower. The spirit, ruach, of “the Lord bloweth upon it,” i.e., “the ‘breath’ of God the Creator, which pervades the creation, generating life, sustaining life, and destroying life, and whose most characteristic elementary manifestation is the wind.” The verse goes on to say that the people or the human race are the perishable grass; “such grass withereth and such flower fadeth, but the word of our God (Jehovah, the God of His people and of sacred history)” יקום לעולם “shall stand forever.” The word “rises up without withering or fading, and endures forever, fulfilling and verifying itself through all times.” Keil and Delitzsch continue,
If this word of God generally has an eternal duration, more especially is this case with the word of the parousia of God the Redeemer, the word in which all the words of God are yea and amen. The imperishable nature of this word, however, has for its dark foil the perishable nature of all flesh, and all the beauty thereof. The oppressors of Israel are mortal, and chesed with which they impose and bribe the perishables; but the word of God, with which Israel can console itself, preserves the field, and ensures it a glorious end to its history. Thus, the seal, which the first crier set upon the promise of Jehovah’s speedy coming, in inviolable; and the comfort which the prophets of God are to bring to His people, who have now been suffering so long, is infallibly sure.
The certainty of Christ’s coming and the consolation He will bring as the God of Israel is made “infallibly sure” by the word of God. This is the passage Peter draws upon when writing verse 25, “But the word of the Lord endureth for ever.” From the pen of Isaiah, the truth of chapter 40 is referred to by Peter within a New Testament, salvific context. The gospel that is preached by Peter is the imperishable, infallibly sure word of God, the same word Isaiah wrote of Christ’s coming bringing hope and security to the Israeli people. Peter’s word of God “which liveth and abideth forever” is Isaiah’s word of God which “shall stand forever.”
Note that the eternal word is tied directly to promise of Christ bringing spiritual renewal in Isaiah 40:30-31 and the promise of being born again in 1 Peter 1:23. Considering this connection in the light of Isaiah 59:21, the dynamic between the Spirit, Word, and believer at work in the flow of redemptive history is unmistakably demonstrated.
 Keil, Delitzsch, Isaiah, 143.
 Keil, Delitzsch, Isaiah, 143. For the comparison of man with flowers and grass see Isa. 37:27, Job 8:11-12, and 14:2, Psalm 90:5-6
 Keil, Delitzsch, Isaiah, 144.
 Keil, Delitzsch, Isaiah, 144.
 Keil, Delitzsch, Isaiah, 144-145.