Understanding the role of the Holy Spirit in the life of the believer is the most important concept the believer needs to understand in his walk as a Christian
It is the work of the Holy Spirit that draws a person to Jesus Christ. Once that person has accepted the atoning work of Jesus as the Messiah, it is the work of the Holy Spirit that reveals the Word of God (the Bible) to the believer. If you seek after any one thing in your role as a believer, seek after the Holy Spirit. It is He who will show you all things.
The Holy Spirit is the third person of the Trinity. Therefore the Holy Spirit is God.
And when they did not agree among themselves they departed after Paul spoke one final word: “The Holy Spirit rightly spoke by the prophet Isaiah to our fathers… —Acts 28:25
The Holy Spirit resides in the believer in the age of the New Testament just like God dwelled in the Temple in the Old Testament. The absence of the Holy Spirit in a person’s life is proof of an unsaved person. Part of the work of the Holy Spirit is to seal the individual believer as to designate the believer as belonging to God.
21 But it is God who establishes us with you in Christ and anointed us is God, 22 who has also sealed us and given us a down payment of the Spirit in our hearts. —2 Corinthians 1:21-22
The Holy Spirit resides inside the believer as the believer is the temple of God.
Or do you not know that your body is the temple of the Holy Spirit who is in you, whom you have from God, and you are not your own. —1 Corinthians 6:19
The Holy Spirit gives gifts and certain abilities to New Testament believers as described in 1 Corinthians 12.
But the manifestation of the Spirit is given to every man for the profit of all. —1 Corinthians 12:7