Carnality comes from the word for flesh, sarkikos, and by extension often refers to man living apart from God’s power and word, whether a believer or unbeliever. When one lives by his own power, he is living by his human fallen nature, which works through the flesh or body. The believer who lives by his human nature instead of by the Holy Spirit is said to be carnal.  The central passage is 1 Corinthians 3:1-3;

Brothers and sisters, I could not address you as people who live by the Spirit but as people who are still worldly—mere infants in Christ.² I gave you milk, not solid food, for you were not yet ready for it. Indeed, you are still not ready.³ You are still worldly. For since there is jealousy and quarrelling among you, are you not worldly? Are you not acting like mere humans?

Where believers are living like unbelievers and are called carnal.

Galatians 5:16-21;

¹⁶ So I say, walk by the Spirit, and you will not gratify the desires of the flesh.¹⁷ For the flesh desires what is contrary to the Spirit, and the Spirit what is contrary to the flesh. They are in conflict with each other, so that you are not to do whatever^[a] you want.¹⁸ But if you are led by the Spirit, you are not under the law.

¹⁹ The acts of the flesh are obvious: sexual immorality, impurity and debauchery;²⁰ idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions²¹ and envy; drunkenness, orgies, and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God.

States the conflict between the flesh and the Holy Spirit, and gives some works of the flesh that are sins. Carnality is opposite to spirituality. Confession of sin to God restores the believer to walking in the light, to fellowship,

1 John 1;

That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked at and our hands have touched—this we proclaim concerning the Word of life.² The life appeared; we have seen it and testify to it, and we proclaim to you the eternal life, which was with the Father and has appeared to us.³ We proclaim to you what we have seen and heard, so that you also may have fellowship with us. And our fellowship is with the Father and with his Son, Jesus Christ.⁴ We write this to make our^[a] joy complete.

⁵ This is the message we have heard from him and declare to you: God is light; in him there is no darkness at all.⁶ If we claim to have fellowship with him and yet walk in the darkness, we lie and do not live out the truth.⁷ But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus, his Son, purifies us from all^[b] sin.

⁸ If we claim to be without sin, we deceive ourselves and the truth is not in us.⁹ If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness.¹⁰ If we claim we have not sinned, we make him out to be a liar and his word is not in us.

And to walking by the Holy Spirit.

Galatians 5;

It is for freedom that Christ has set us free. Stand firm, then, and do not let yourselves be burdened again by a yoke of slavery.

² Mark my words! I, Paul, tell you that if you let yourselves be circumcised, Christ will be of no value to you at all.³ Again I declare to every man who lets himself be circumcised that he is obligated to obey the whole law.⁴ You who are trying to be justified by the law have been alienated from Christ; you have fallen away from grace.⁵ For through the Spirit we eagerly await by faith the righteousness for which we hope.⁶ For in Christ Jesus neither circumcision nor uncircumcision has any value. The only thing that counts is faith expressing itself through love.

⁷ You were running a good race. Who cut in on you to keep you from obeying the truth?⁸ That kind of persuasion does not come from the one who calls you.⁹ “A little yeast works through the whole batch of dough.”¹⁰ I am confident in the Lord that you will take no other view. The one who is throwing you into confusion, whoever that may be, will have to pay the penalty.¹¹ Brothers and sisters, if I am still preaching circumcision, why am I still being persecuted? In that case the offense of the cross has been abolished.¹² As for those agitators, I wish they would go the whole way and emasculate themselves!

¹³ You, my brothers and sisters, were called to be free. But do not use your freedom to indulge the flesh^[a]; rather, serve one another humbly in love.¹⁴ For the entire law is fulfilled in keeping this one command: “Love your neighbor as yourself.”^[b]15 If you bite and devour each other, watch out or you will be destroyed by each other.

¹⁶ So I say, walk by the Spirit, and you will not gratify the desires of the flesh.¹⁷ For the flesh desires what is contrary to the Spirit, and the Spirit what is contrary to the flesh. They are in conflict with each other, so that you are not to do whatever^[c] you want.¹⁸ But if you are led by the Spirit, you are not under the law.

¹⁹ The acts of the flesh are obvious: sexual immorality, impurity and debauchery;²⁰ idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions²¹ and envy; drunkenness, orgies, and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God.

²² But the fruit of the Spirit is love, joy, peace, forbearance, kindness, goodness, faithfulness,²³ gentleness and self-control. Against such things there is no law.²⁴ Those who belong to Christ Jesus have crucified the flesh with its passions and desires.²⁵ Since we live by the Spirit, let us keep in step with the Spirit.²⁶ Let us not become conceited, provoking and envying each other.