“But I say, 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. Now the works of the flesh are evident: sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions, envy, drunkenness, orgies, and things like these. I warn you, as I warned you before, that those who do such things will not inherit the kingdom of God. But 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.” Galatians 5:16-26 (ESV)
What more needs to be said? The contrast between how the world lives and how those with the Holy Spirit live is seen in these verses. How do we know that we have the Holy Spirit? It will be evident by the works that we do. If we do things that are impure, sensual, idolatrous, or that cause strife, divisions, and dissension, then it is evident that we are in the flesh and not the Spirit. Christians will still sin after salvation, but the pattern will change as the Holy Spirit works in us, convicting us of sin and growing us in the fruits of love, joy, peace, and so forth. The more we grow in holiness, the more we mourn our sin.