16 I say then: Walk in the Spirit, and you shall not fulfill the lust of the flesh. 17 For the flesh lusts against the Spirit, and the Spirit against the flesh; and these are contrary to one another, so that you do not do the things that you wish. 18 But if you are led by the Spirit, you are not under the law.
In the book of Galatians Paul is confronting a group of Jews who were trying to make the Gentiles adhere to the letter of the law. Paul tells them that they were set free from the law and therefore do not need to step back into that bondage. Here Paul offers the counter solution to living under the law:
Walk in the Spirit
In the old testament the way to not walk in sin (or in the flesh) was to follow the law. However, as the Bible shows, this was not enough to counter the carnal nature in us. We needed the sacrifice of Jesus on the cross to set us free and then we needed the constant presence of the Holy Spirit in us. Paul says that there is no need to go back to the bondage of living under the law but instead all we need to do is walk in the Spirit.
Notice where the focus is in this verse. The focus is not on the flesh or the sinful nature but on the Spirit. In other words we should not be focusing on not sinning, we should be focusing on walking in the Spirit. As he continues in the chapter he does list the "works of the flesh" (Gal 5:19-21) but then counters that list with the "fruits of the spirit" (Gal 5:22-23). But our focus should be on exhibiting the fruits of the Spirit, not on trying stop the works of the flesh.
As Paul says if we walk in the spirit we will not fulfill the lust of the flesh.
It is that simple! So many people waste years of their life fighting to stop sinning and all they had to do was start focusing on walking in the Spirit. Of course to truly walk in the Spirit does take sacrifice. It takes making decisions to feed the Spirit when it is easier to feed the flesh. It takes making decision to get in the Word instead of watching a movie. To spend time in worship rather than listening to songs focused on fleshly desires. It is simple but it is not always easy. However it is definitely worth it!