Walk in the Spirit

There are two ways to walk:
1) Walk in the Spirit
2) Walk in the flesh

The Bible is quite clear how we should walk.

This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh.
- Galatians 5:16 (KJV)

The flesh is lawlessness, and by that definition, opposite to the Spirit.

For they that are after the flesh do mind the things of the flesh; but they that are after the Spirit the things of the Spirit. For to be carnally minded is death; but to be spiritually minded is life and peace. Because the carnal mind is enmity against God: for it is not subject to the law of God, neither indeed can be. So then they that are in the flesh cannot please God.
- Romans 8:5-8 (KJV)

The flesh is hostile towards God.

Also, the lust of the flesh can not be fulfilled. There's always something else it wants.

There is a conflict between walking in the Spirit, and walking in the flesh. New-born Christians have both, and must choose between them every day.

In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise, Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.
- Ephesians 1:13-14 (KJV)

The wicked don't have the Spirit, and just do what they want (or think is "right").

We all veer of from the narrow path at some point or another, and normally God will give us time to find our way back, but if this takes too long (or is not happening at all), God will intervene.

This charge I commit unto thee, son Timothy, according to the prophecies which went before on thee, that thou by them mightest war a good warfare; Holding faith, and a good conscience; which some having put away concerning faith have made shipwreck: Of whom is Hymenaeus and Alexander; whom I have delivered unto Satan, that they may learn not to blaspheme.
- 1 Timothy 1:18-20 (KJV)

Firstly, note that it's a lesson. Not a permanent thing in other words.

Secondly, it appears quite rough (to be delivered to satan).

Blasphemy can be seen as pushing the Spirit of God away. This is what happens when we walk in the flesh. We're essentially pushing the Spirit of God away, and follow the lust of the flesh instead.

The following verse also talks about being delivered to satan.

In the name of our Lord Jesus Christ, when ye are gathered together, and my spirit, with the power of our Lord Jesus Christ, To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
- 1 Corinthians 5:4-5 (KJV)

Here we see that we are delivered to satan for the purpose of destruction of the flesh. Satan is the ruler over the flesh, and God is merely saying "That's who you're following. Are you sure about that?".

This kind of punishment can be in all sorts of shapes and forms, and serves as a big wake up call, e.g. to be taught not to push the Spirit of God away by walking in the flesh. It's one or the other. Huge lesson.

There is a limit as to how long the Spirit of God will strive with you though.

In every age there is given to men their day of light and privilege, a probationary time in which they may become reconciled to God. But there is a limit to this grace. Mercy may plead for years and be slighted and rejected; but there comes a time when mercy makes her last plea. The heart becomes so hardened that it ceases to respond to the Spirit of God. Then the sweet, winning voice entreats the sinner no longer, and reproofs and warnings cease.
- Ellen White, Desire of Ages, 587.1

When you keep pushing the Spirit of God away, you commit the unpardonable sin.

Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men.
- Matthew 12:31 (KJV)

Do not be discouraged when you are rebuked by the Lord, for He only rebukes the ones He loves.

For consider him that endured such contradiction of sinners against himself, lest ye be wearied and faint in your minds. Ye have not yet resisted unto blood, striving against sin. And ye have forgotten the exhortation which speaketh unto you as unto children, My son, despise not thou the chastening of the Lord, nor faint when thou art rebuked of him: For whom the Lord loveth he chasteneth, and scourgeth every son whom he receiveth. If ye endure chastening, God dealeth with you as with sons; for what son is he whom the father chasteneth not? But if ye be without chastisement, whereof all are partakers, then are ye bastards, and not sons. Furthermore we have had fathers of our flesh which corrected us, and we gave them reverence: shall we not much rather be in subjection unto the Father of spirits, and live? For they verily for a few days chastened us after their own pleasure; but he for our profit, that we might be partakers of his holiness. Now no chastening for the present seemeth to be joyous, but grievous: nevertheless afterward it yieldeth the peaceable fruit of righteousness unto them which are exercised thereby.
- Hebrews 12:3-11 (KJV)

When we walk in the Spirit (pray, fast, study, etc) we are said to have crucified the flesh. Just like Jesus did on the cross.

And he said to them all, If any man will come after me, let him deny himself, and take up his cross daily, and follow me.
- Luke 9:23 (KJV)

Paul referred to this as "dying daily".

I protest by your rejoicing which I have in Christ Jesus our Lord, I die daily.
- 1 Corinthians 15:31 (KJV)

The fruit of the Spirit outweighs the works of the flesh.

Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God. But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith, Meekness, temperance: against such there is no law. And they that are Christ's have crucified the flesh with the affections and lusts. If we live in the Spirit, let us also walk in the Spirit. Let us not be desirous of vain glory, provoking one another, envying one another.
- Galatians 5:19-26 (KJV)

To walk in the Spirit, means to be closer to God.

To walk in the flesh, means you will end up with a hardened heart.

For, brethren, ye have been called unto liberty; only use not liberty for an occasion to the flesh, but by love serve one another.
- Galatians 5:13 (KJV)