The Holy Spirit, the third Person of the Triune God has a specific function within the Godhead and our lives. He is promised to be present WITH believers: 

John 16:7 But I tell you the truth: It is for your good that I am going away. Unless I go away, the Counselor will not come to you; but if I go, I will send him to you.

He is promised to be IN you:
John 14:17 But you know him, for he lives with you and will be in you.
1 Cor. 6:19 Do you not know that your body is a temple of the Holy Spirit, who is in you, whom you have received from God? 
Rom. 8:9 And if anyone does not have the Spirit of Christ, he does not belong to Christ.
Acts 7:55 But Stephen, full of the Holy Spirit, looked up to heaven and saw the glory of God, and Jesus standing at the right hand of God.

The Holy Spirit's Primary Purposes Include:

1. To Draw Attention To Jesus - John 16:14 He will bring glory to me by taking from what is mine and making it known to you. 15All that belongs to the Father is mine. That is why I said the Spirit will take from what is mine and make it known to you.

2. To Bring Conviction - John 16:8 When he comes, he will convict the world of guilt in regard to sin and righteousness and judgment

3. To Reveal Truth - John 16:13 But when he, the Spirit of truth, comes, he will guide you into all truth. He will not speak on his own; he will speak only what he hears, and he will tell you what is yet to come.

4. To Give Power To Draw Attention To Jesus - Acts 1:8 But you will receive power when the Holy Spirit comes on you; and you will be my witnesses in Jerusalem, and in all Judea and Samaria, and to the ends of the earth.”

5. To Baptize Believers - Acts 19:1 While Apollos was at Corinth, Paul took the road through the interior and arrived at Ephesus. There he found some disciples 2and asked them, “Did you receive the Holy Spirit when£ you believed?”  They answered, “No, we have not even heard that there is a Holy Spirit.” 3So Paul asked, “Then what baptism did you receive?” “John’s baptism,” they replied. 4Paul said, “John’s baptism was a baptism of repentance. He told the people to believe in the one coming after him, that is, in Jesus.” 5On hearing this, they were baptized into£ the name of the Lord Jesus. 6When Paul placed his hands on them, the Holy Spirit came on them, and they spoke in tongues£ and prophesied. 7There were about twelve men in all.

6. To Deposit Supernatural Gifts - 1 Cor. 12:1 Now about spiritual gifts, brothers, I do not want you to be ignorant; 1 Cor. 12:7 Now to each one the manifestation of the Spirit is given for the common good.; • 1 Cor. 14:1 Follow the way of love and eagerly desire spiritual gifts, especially the gift of prophecy.; 1 Cor. 14:12 So it is with you. Since you are eager to have spiritual gifts, try to excel in gifts that build up the church.