Chapter forty of Isaiah unveils what man really is and what man really needs. The prophet's speaking in this chapter surely is an excellent example of preaching the gospel.
Verses 6 through 8 say, "All flesh is grass / And all its beauty is like the flower of the field; / The grass withers, the flower fades, / Because the breath of Jehovah blows upon it. / Surely the people are grass. / The grass withers and the flower fades, / But the word of our God will stand forever." Here Isaiah compares fading men of flesh to the word of God. What will remain among the human race? Everything will fade and wither except the word of God. This word is actually Christ, the glory of Jehovah. All men are fading, but Christ as the living word will remain.
Isaiah 40:6-8 indicates that all men of flesh should receive the living and abiding word of God to be regenerated that they may have the eternal life to live forever (1 Pet. 1:23-24).
Isaiah 40 also reveals that all men are like a drop from a bucket and are accounted as specks of dust on the scales (v. 15a). All men are as nothing before God; they are accounted as less than nothing and vanity (v. 17). All the inhabitants of the earth are like grasshoppers (v. 22a).
This chapter indicates that man cannot be compared to God, who is great, who takes up the islands as very fine powder, who sits above the circle of the earth, who stretches out the heavens like a curtain and spreads them out like a tent, and who brings the princes to nought and makes the judges of the earth as nothing (vv. 15b-18, 22-26).
This chapter tells us not only what man is but also what man needs.