In short, what you will find in the Scriptures is this: Wherever flesh is treated as in opposition to spirit, you can generally take flesh to mean everything that is contrary to the Spirit, as [in John 6:63]: “The flesh is of no avail.” But where flesh is treated on its own, you may take it that it signifies the bodily constitution and nature, as for example: “They shall be two in one flesh” [Matt. 19:5]; “My flesh is food indeed” [John 6:55]; or “The Word became flesh” [John 1:14]. In these passages you can drop the Hebraism and say “body” instead of “flesh,” for the Hebrew language has only the one word “flesh” for what we express by the two words “flesh” and “body,” and I wish this distinction of terms had been observed in translation throughout the whole canon of Scripture. My passage from Genesis 6, will thus, I think, still stand firmly against free choice, when free choice is proved to be flesh, which Paul in Romans 8[:7] says cannot submit to God (as we shall see in that passage), and which Diatribe herself says can will nothing good.
The Bondage of the Will
Luther’s Works Vol. 33