Isaiah 40:6
4 Every valley must be elevated and every mountain and hill leveled. The rough terrain will become a level plain, the rugged landscape a wide valley. 5 The splendor of the Lord will be revealed, and all people will see it at the same time. For the Lord has decreed it.” 6 A voice says, “Cry out!” Another asks, “What should I cry out?” The first voice responds: “All people are like grass, and all their promises are like the flowers in the field. 7 The grass dries up, the flowers wither, when the wind sent by the Lord blows on them. Surely humanity is like grass. 8 The grass dries up, the flowers wither, but the decree of our God is forever reliable.”
1 Peter 1:24
22 You have purified your souls by obeying the truth in order to show sincere mutual love. So love one another earnestly from a pure heart. 23 You have been born anew, not from perishable but from imperishable seed, through the living and enduring word of God. 24 For all flesh is like grass and all its glory like the flower of the grass; the grass withers and the flower falls off, 25 but the word of the Lord endures forever. And this is the word that was proclaimed to you.
Notes and References
"... Flesh as a Morally Neutral Term ... The phrase “all flesh” occurs twice in New Testament citations of the Old Testament (Acts 2:17 cites Joel 3:1; 1 Peter 1:24 cites Isaiah 40:6). In both cases the phrase refers to all of humanity. In 1 Peter 1:24 the emphasis seems to be on the temporality of humankind when compared with the eternal word of God. Sometimes the term flesh is neutral but qualified by an adjective or phrase that gives the concept negative nuances, e.g., 1 John 2:16, “the lust of the flesh,” or 2 Peter 2:10, “those who go after other flesh,” or 2:18, “the sensual desires of the flesh” (compare Jude 7, 8, 23) ..."
Martin, Ralph P. Dictionary of the Later New Testament & Its Developments (p. 579) InterVarsity Press, 1997