Isaiah 31:3 juxtaposes “flesh” and “spirit” in a way that seems very similar to Paul.

Egypt is human (אָדָם) and not God (אֵל), and their horses are flesh (בָּשָׂר) and not spirit (רוּחַ) … (Is 31:3)

The Juxtaposition

Notice how the concepts juxtaposed are even broader than flesh and spirit.

Don’t Trust	Trust
Egypt	Yahweh
Humanity	God
Flesh	Spirit

Isaiah 31 is about faith in Yahweh. Isaiah’s point is that in the face of Assyrian exile, the faithful remnant must trust Yahweh/God/Spirit and not Egypt/humanity/flesh.

It sounds very similar to many places in Paul, like Romans 8:6:

For the mind set on the flesh is death, but the mind set on the Spirit is life and peace.

Eschatological Context

Furthermore, the prophetic vision is thoroughly eschatological, looking ahead to “that day” (בַּיּוֹם הַהוּא, Is 31:7). Isaiah calls Israel to turn to the one against whom they have rebelled (Is 31:6) and trust that on “that day” Yahweh will bring justice, protection, and peace (Is 31:5–9). McConville comments,

A picture of the eschatological faithfulness of a people that has rid itself of the paraphernalia of falsehood is merged with exhortation firmly in the present. Hope for the future functions as command for the here and now.¹

Broader Messianic Context

One final note: the broader context is thoroughly messianic. Chapter 31 flows right into Isaiah 32, which opens with these words:

Look, a king will reign righteously … (Is 32:1)

This king brings healing, a clear vision of what is true and good (Is 32:1–8). The complacent are commanded to mourn because the king also brings justice, which leads to destruction for some (Is 32:9–14). The destruction will remain …

Until the Spirit (רוּחַ) is poured out upon us … (Is 32:15)

When רוּחַ is poured out, creation changes: justice leads to righteousness, which leads to peace and trust.

Conclusion

When you zoom out just a bit, considering both Isaiah 31 and 32, you see that the juxtaposition includes several concepts, much more than “flesh” and “spirit”:

Don’t Trust	Trust
Egypt (ch. 31)	Yahweh (ch. 31)
Humanity (ch. 31)	God (ch. 31)
Flesh (ch. 31)	Spirit (ch. 31)
Status quo of complacency (ch. 32)	Coming king (ch. 32)
Exultant cities of abundance (ch. 32)	Coming new creation (ch. 32)

I don’t know why this text doesn’t get more attention in discussions of flesh and spirit in Paul.

1. J. Gordon McConville, Isaiah, Baker Commentary on the Old Testament: Prophetic Books (Grand Rapids, MI: Baker Academic, 2023), 361. ↩