What does it mean to be walking in the flesh and walking in the Spirit? What can the Bible tell us about the differences between the two?
Walking in the Spirit
Paul addresses walking in the Spirit with a capital “S” which means that the word Spirit is a proper noun meaning this is God the Holy Spirit as we can tell in Colossians 1:9-10 “And so, from the day we heard, we have not ceased to pray for you, asking that you may be filled with the knowledge of his will in all spiritual wisdom and understanding, so as to walk in a manner worthy of the Lord, fully pleasing to him, bearing fruit in every good work and increasing in the knowledge of God.” If a believer is walking “in a manner worthy of the Lord” and is “fully pleasing to Him” then they will be “bearing fruit in every good work and increasing in the knowledge of God” so someone who is walking in the Spirit of God will be producing good fruit proving that he or she is walking in the Spirit  and that they will also be “increasing in the knowledge of God.” This means that they will necessarily have a thirst and hunger for the Word of God and be reading their Bible, studying the Word, hearing biblical teachings, and as a consequence, growing in the knowledge of God. David had this hunger and thirst too which is why he wrote in Psalm 42:1-2 that “As a deer pants for flowing streams, so pants my soul for you, O God. My soul thirsts for God, for the living God.” This gives us an image of a deer that has been running toward the flowing streams, which is indicative of having a thirst not only for God’s Word but for righteousness. This is joined with a hunger for God and anyone who hungers after God is devouring the Word of God, which is the daily bread we all need to sustain us in our daily walk with God. Charles Spurgeon said that “We are not justified by the manner of our walk, but by our being in Christ Jesus.”
Walking in the Flesh
Paul tells the Galatian’s that “the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law. And those who belong to Christ Jesus have crucified the flesh with its passions and desires. If we live by the Spirit, let us also keep in step with the Spirit. Let us not become conceited, provoking one another, envying one another” (Gal 5:22-25). The same thing as living by the Spirit or keeping “in step with the Spirit” is walking in the Spirit or being controlled by the Spirit of God by not yielding our bodies to “the flesh with its passions and desires.” Paul reveals the evidence of a believer is faithfulness, gentleness, self-control and other such fruits and that “those who belong to Christ Jesus have crucified the flesh with its passions and desires.” If they haven’t then they won’t be crucifying the flesh but walking in the flesh. By walking “by the Spirit” we won’t “gratify the desires of the flesh” (Gal 5:16). When we’re not walking in the Spirit of God, we will be gratifying the desires of the flesh so that’s the difference between walking in the Spirit and walking in the flesh. The fruits or works we produce give evidence of whether we are walking in the Spirit or walking in the flesh.  That’s how we can know that we are or we are not walking in the Spirit. That’s why Paul wrote “For though we walk in the flesh, we are not waging war according to the flesh” (2 Cor 10:3) because “our warfare are not of the flesh but have divine power to destroy strongholds” (2 Cor 10:4).
Consequences of Walking in the Flesh
Paul had great concern for all the churches that they not walk in the flesh because the consequences are most severe and that includes the wages of this walk, which is death (Rom 6:23). He continues in Romans 8:4b-8 by saying in Jesus “he condemned sin in the flesh” (Rom 8:3c) so we must “walk not according to the flesh but according to the Spirit. For those who live according to the flesh set their minds on the things of the flesh, but those who live according to the Spirit set their minds on the things of the Spirit. For to set the mind on the flesh is death, but to set the mind on the Spirit is life and peace. For the mind that is set on the flesh is hostile to God, for it does not submit to God’s law; indeed, it cannot. Those who are in the flesh cannot please God.”
By Jesus’ death for us “we are debtors, not to the flesh, to live according to the flesh. For if you live according to the flesh you will die, but if by the Spirit you put to death the deeds of the body, you will live. For all who are led by the Spirit of God are sons of God” (Rom 8:12-14) so living by the flesh results in death but if you are walking “by the Spirit” you will “put to death the deeds of the body (or flesh)” and live. Paul was persuaded of better things concerning the Christians in Rome because he said “You, however, are not in the flesh but in the Spirit, if in fact the Spirit of God dwells in you” however “Anyone who does not have the Spirit of Christ does not belong to him” (Rom 8:9).
Walking in the Spirit or the Flesh?
Getting back to Paul’s letter to the Galatians he tells them to “walk by the Spirit, and you will not gratify the desires of the flesh. For the desires of the flesh are against the Spirit, and the desires of the Spirit are against the flesh, for these are opposed to each other, to keep you from doing the things you want to do. But if you are led by the Spirit, you are not under the law” (Gal 5:16-18). If we are walking in the Spirit or as Paul commands the church “walk by the Spirit” which is the same thing, we will not be “gratifying the desires of the flesh.” The converse is true…if we are not walking in the Spirit, then we will be walking in the flesh and producing “the works of the flesh [which] are evident: sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions, envy, drunkenness, orgies, and things like these.” (Gal 5:19-21a). Our works or fruits show which spirit we are walking in…either works of the Spirit or works of the flesh.
Five Differences Between Walking in the Flesh and in the Spirit
To sum it up we can see evidence of whether or not we are walking in the flesh or the Spirit as follows:
- Those who have the Spirit of God produce fruits that reveal whether they are a child of God or not. If there are no Spiritual fruits, then God is not their Father.
- Those who walk in the Spirit have crucified the flesh and do not submit themselves to the desires of the flesh but those who don’t walk in the Spirit grieve the Spirit and their works producing nothing more than the wages that they have earned and that is death (Rom 6:23).
- Those who walk in the flesh live according to the flesh prove that they do by their works but those with the Spirit of God  prove that they are Christ’s by producing a Christ-like life.
- Those who walk in the flesh produce the fruits of the flesh like sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions, envy, drunkenness, orgies, and things like these” (Gal 5:20-21a) but those who walk in the Spirit “will not gratify the desires of the flesh” (Gal 5:16).
- Those who “put to death the deeds of the body (or flesh)” (Rom 8:13) are truly walking in the Spirit but those who do not have the Spirit of Christ assuredly do “not belong to him” (Rom 8:9).
If you have never been born again (John3:3) then you have the wrath of God abiding on you (John 3:18, 3:36b) and not one of your best works can ever please God because “Those who are in the flesh cannot please God” (Rom 8:8). Since you have rejected Christ, if indeed you have, you reject your only hope of eternal life and have standing before you the eternal state of the wages that you have earned (Rom 6:23). Because everyone has sinned (Rom 3:23) Jesus came to earth and was born of a virgin, lived a sinless life but became sin for us so that when God the Father looks at us, He doesn’t see our sinfulness but He sees the righteousness of Christ and He imputes His righteousness to us (2 Cor 5:21). Today, if you have heard His voice, repent and trust in Him because today can be your day of salvation (2 Cor 6:2). If not and Jesus returns before you are born again, you face a Christ-less eternity and the everlasting wrath of God (Rev 20:11-15).
More about the Fruit of the Spirit: Fruit of the Spirit list 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), copyright © 2001 by Crossway, a publishing ministry of Good News Publishers. Used by permission. All rights reserved.