These verses can be easily misunderstood -- and in fact they are misunderstood by some.
So what do they teach and how does that fit in with the fact that the old nature ("the flesh") has not been eradicated after the New Birth, and therefore there is a conflict between the spirit and the flesh, or the indwelling Holy Spirit and the flesh?
1. When a person is born again, his/her spirit is *quickened* or made alive by the power of the Holy Spirit. The Holy Spirit takes up residence within our spirits, and we become children of God.
2. The Bible says that if any man be in Christ he is a "new creature" (or creation). Old things have passed away, and all things have become new. Therefore the new nature is indeed the quickened spirit, which desires to serve, please and obey God. And it is this "seed" which the apostle John speak of. This new nature abhors sin, since God gives the believer a new heart and a new spirit. Indeed the new nature cannot sin (as John says).
3. At the same time, God does not automatically remove the flesh (the sin nature which is within the soul). Therefore Christians can and do sin.
4. However, Paul says that "sin shall NOT have dominion over you" which means that no believer can be dominated by his/her old nature. And in order to keep the old nature under subjection, Christians are commanded to crucify (or mortify = put to death) the flesh. Christians do not have an excuse to sin, neither is salvation a license to sin.
5. Paul shows us the conflict between the Spirit and the flesh in Galatians 5, since this is real and it is true:
GALATIANS 5: CHRISTIANS ARE COMMANDED TO WALK IN THE SPIRIT
16 This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh.
17 For the flesh lusteth [craves sin] against the Spirit, and the Spirit [wars] against the flesh: and these are contrary [in conflict with] the one to the other: so that ye cannot do the things that ye would. 18 But if ye be led of the Spirit, ye are not under the law.
THE WORKS (SINS) OF THE FLESH
19 Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, 20 Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, 21 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.
THE FRUIT (ATTITUDES) OF THE SPIRIT
22 But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith, 23 Meekness, temperance: against such there is no law.
THE FLESH MUST BE CRUCIFIED (PUT TO DEATH)
24 And they that are Christ's have crucified the flesh with the affections and lusts.25 If we live in the Spirit, let us also walk in the Spirit.