In this passage, Fee discusses Galatians 5:16–18, “But I say, live by the Spirit and you will not carry out the desires of the flesh. For the flesh has desires that are opposed to the Spirit, and the Spirit has desires that are opposed to the flesh, for these are in opposition to each other, so that you cannot do what you want. But if you are led by the Spirit, you are not under the law.”
Fee makes a great point that the command “walk by the Spirit” is an imperative and not a passive indicative (“you will be led by the Spirit”).
That leads finally to the question that is less exegetical than existential. 'That is all fine and good,' it is often said, 'but how does one go about walking in the Spirit' so as not to live from the perspective of the flesh? The best answer to that question is still the exegetical one, not the existential or formulaic one. Paul, of course, is speaking from within a historical context in which the Spirit was the primary, experienced reality in the Christian life, as 3:2–5 has made plain. This appeal to the Galatians, therefore, is just that, an appeal to 'go on walking by the very same Spirit by which you came to faith and with whom God still richly supplies you, including by the working of miracles in your midst.' That is, a powerful and experiential--supernatural, if you will--presuppositional base lies behind this imperative.
But it comes by way of imperative, not by way of passive indicative (as in v. 18). Life in the Spirit is not passive submission to the Spirit to do a supernatural work in one's life; rather, it requires conscious effort, so that the indwelling Spirit may accomplish his ends in one's life. One is urged to 'walk by the Spirit' or 'live by the Spirit' by deliberately 'conforming one's life to the Spirit' (v. 25). If such a person is also described as being 'led by the Spirit,' that does no mean passively; it means to rise up and follow the Spirit by walking in obedience to the Spirit's desire. (433)
One of the things that I struggle with in Reformed theology and other monergistic systems is the question, “Why does Christian A grow when Christian B does not?” In a monergistic system, the answer has to be “Because God empowers Christian A to grow and He does not empower Christian B to grow.” That sucks for Christian B.
I think Galatians 5 shows that Paul was more synergistic in his understanding of spiritual growth. Sure, spirituality is a work of the Spirit. We can’t grow ourselves by shear will power. But we can resist the Spirit, and we do have the responsibility to walk in the Spirit.