The difference between living by and walking by the Spirit

Question

Galatians 5:25 (NASB) says:

"If we live by the Spirit, let us also walk by the Spirit."

What is the difference between living by the Spirit and walking by the Spirit?

Answer 1

To be very succinct:
Living in the spirit is about faith, walking in the spirit is about what we practice.

Living in the Spirit

Fortunately, Paul did us a great service of defining the terms!

Early in the letter to the Galatians, we see this passage:

Galations 2:19-20 (NASB)
19 For through the Law I died to the Law, so that I might live to God. 20 I have been crucified with Christ; and it is no longer I who live, but Christ lives in me; and the life which I now live in the flesh I live by faith in the Son of God, who loved me and gave Himself up for me.

What Paul is saying here that life in God (or, as he later refers to it, living in the spirit) is still living in the flesh (meaning living in our current bodies), but living by faith in the Son of God.

Walking in the Spirit

Galations 5:16-21 (NASB)
16 But I say, walk by the Spirit, and you will not carry out the desire of the flesh. 17 For the flesh sets its desire against the Spirit, and the Spirit against the flesh; for these are in opposition to one another, so that you may not do the things that you please. 18 But if you are led by the Spirit, you are not under the Law. 19 Now the deeds of the flesh are evident, which are: immorality, impurity, sensuality, 20 idolatry, sorcery, enmities, strife, jealousy, outbursts of anger, disputes, dissensions, factions, 21 envying, drunkenness, carousing, and things like these, of which I forewarn you, just as I have forewarned you, that those who practice such things will not inherit the kingdom of God.

The idea in this passage is that if we are walking in the flesh, then we practice desires of the flesh. When we walk in the flesh, we will practice immorality, practice jealousy, we will have outbursts of anger, we will practice drunkenness, etc.

Summary

Essentially, "living in the spirit" comes down to having faith in God (that is, having an active belief and trust in God). "Walking in the spirit" comes down to what we focus on and what we practice (ie, the acts that we continually think about and commit).

Answer 2

In Galatians 5:25, "live" is "live" as in "live or die" rather than "live" as in "the way I live my life". In other words, "If the Spirit is what saves us from death, let us allow that same Spirit to direct our steps"

This is reinforced in chapter 6 with a different metaphor:

⁸ For the one who sows to his own flesh will from the flesh reap corruption, but the one who sows to the Spirit will from the Spirit reap eternal life.   _NASB