The expression “the flesh” often carries a special doctrinal meaning in the NT. In this usage it does not refer to the body, but to the old nature of the believer, with its tendency to sin even after the miracle of the new birth.
While believers should be spiritual, some are fleshly or carnal, 1 Cor. 3:1. These individuals are said to walk according to the flesh, 2 Cor. 10:2. They serve the law of sin, Rom. 7:25. Walking in the flesh is contrasted with walking in the Spirit, Rom. 8:4, 5.
Christians are admonished to make no provision for the flesh, Rom. 13:14, and its filthiness, 2 Cor. 7:1. A dreadful list of the works of the flesh appears in Gal. 5:19-21. They that are “in the flesh” cannot please God; their minds are at enmity with Him, Rom. 8:7, 8. The flesh is contrary to the Spirit, Gal. 5:17. No good thing dwells in the flesh, Rom. 7:18.
The notion that spiritual Christians may eradicate the old nature by a superior form of holiness is in error, 1 John 1:8-10. The teaching of Scripture is that in a believer the flesh is controlled by the Spirit, Gal. 5:16. The secret of this control is found in Rom. 6:6-13. It is based on knowing, v. 6; reckoning, v. 11; and yielding, v. 13. Gal. 5:24 states the result of this victory.
William Evans, The Great Doctrines of the Bible, (Chicago: Bible Institute Colportage Assoc., 1912), WORDsearch CROSS e-book, 291-292.
AMEN.