The Bible often uses the term flesh to illustrate what Jesus strongly warned against: “the spirit is willing but the flesh is weak.” Here the term flesh is used to describe that part of our nature which stands in contrast to our spirit. It is the carnal nature of man, the root of our sinful passions.
Our flesh encompasses body, mind and soul—that part of us which is able to function without ever submitting to God. It’s very important to understand that the flesh follows us into our new life in God. It continues to have a life of its own, even as our spirit made alive.
Regardless of the fact that we’re now focused on the desire of the Spirit, we find ourselves constantly embroiled in a battle with the desires of our flesh, as Paul so emphatically states in Galatians 5:17. Thank God there’s help!
From Free from the Power of Sin: the Keys to Growing in God in Spite of Yourself