The Holy Spirit is an extraordinary gift given to us by God. He was sent to be our counselor and dwells in the hearts, minds and souls of men to help guide us to salvation. All that is required is our cooperation, as man always has free will to disregard the prompts of the Holy Spirit. Yet, the more that man does respond to His prompts, the more the work of the Holy Spirit becomes apparent in the life of that man.
Jesus Himself told the apostles about the role of the Holy Spirit:
1. The Holy Spirit enlightens the world about sin, righteousness and condemnation
John 16:8 And when he comes he will convict the world with regard to sin and righteousness and condemnation.
2. The Holy Spirit is the teacher and reminds the world of the Word of God.
John 14:26 The Advocate, the Holy Spirit that the Father will send in my name—he will teach you everything and remind you of all that [I] told you.
3. Those who follow the guidance of The Holy Spirit will find their hearts changed and they will live like true children of God.
Galatians 5:18:26 But if you are guided by the Spirit, you are not under the law. Now the works of the flesh are obvious: immorality, impurity, licentiousness, idolatry, sorcery, hatreds, rivalry, jealousy, outbursts of fury, acts of selfishness, dissensions, factions, occasions of envy, drinking bouts, orgies, and the like. I warn you, as I warned you before, that those who do such things will not inherit the kingdom of God. In contrast, the fruit of the Spirit is love, joy, peace, patience, kindness, generosity, faithfulness, gentleness, self-control. Against such there is no law. Now those who belong to Christ [Jesus] have crucified their flesh with its passions and desires. If we live in the Spirit, let us also follow the Spirit. Let us not be conceited, provoking one another, envious of one another.