what does the holy spirit do?

Christian Doctrine    Let's Study the Nature of the Holy Spirit - the Third Member of the Holy Trinity      

The Holy Spirit has one essential task: to bear witness to mankind of the Father and the Son.  The Holy Spirit brings us, in our fallen state, to a place where we seek, see, and accept God and Christ as Lord:

...no one can say 'Jesus is Lord' except by the Holy Spirit.  1 Corinthians 12:3b

When He comes, He will convict the world of guilt in regard to sin and righteousness and judgment. "   John 16:8

The Holy Spirit is with us, as the representation of the person of Jesus.  Indeed, Jesus sent Him to us after His ascension, so that we would be 'comforted' as Jesus comforted His followers when He was with mankind.  When Jesus was on earth as a man, He could only be in one place at a time.  The Spirit is the omnipresent, ongoing representation of God to the Christian; He is God living in us, leading us in the ways of Christ:

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."  John 16:7

I will ask the Father, and He will give you another Counselor to be with you forever - the Spirit of Truth.  The world cannot accept Him, because it neither sees Him nor knows Him.  But you know Him, for He lives with you and will be in you.  I will not leave you as orphans; I will come to you.  Before long, the world will not see me anymore, but you will see me."  John 14:16-20a

The Holy Spirit guides the Christian in the ways of God and Christ, prodding and reminding, and convicting of sin.  He keeps us close to the Father, and is the cause of our re-birth in the Spirit:

...if by the Spirit you put to death the misdeeds of the body, you will live, because those who are lead by the Spirit of God are sons of God...you received the Spirit of sonship.  Romans 8:14, 15b

...the Counselor, the Holy Spirit, whom the Father will send in my name, will teach you all things and will remind you of everything I have said to you."  John 14:26

As He does this work in the Christian, many changes come about in the Christian's life.  Evidences of the Spirit's indwelling are noticeable as 'fruit' in the Christian's new life (born again life) that are totally opposite of the 'normal' living of people who do not have the Holy Spirit in their life (non-Christians): 

But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control."  Galatians 5:22-23a

The Holy Spirit is living within us, as any Christian will attest.  The new 'life', the victory over the struggles of the 'old life', the peace that settles our searching and troubled spirits, and the purpose in life that only Christians can claim is the result of the new spiritual birth, caused by the indwelling of God the Holy Spirit.