His ministry in both Old and New Testaments is both vital and life-changing.

In the OT:
Revealer of truth, the Word of God
      To all prophets and men of faith - concerning the now, and the yet to come.
            Also to Pharaoh, Zedekiah, Nebuchadnezzar, Belshazzar ...
                  Is 48, 53  Dan 222,28  Amos 4  Ps 22  Gen 1,3
      The Feasts and sacrifices reveal Christ, God's promised rescue plan.
      God makes himself known to all who call upon him:
            Abel, Enoch, Noah, Abraham, Moses, David ...
The Spirit of the Lord  will come to free, heal, bring life.  Is 61  Ezek 37
      He will create a righteous kingdom.  1Sam 161-13  2 Sam 231-5  Dan 235, 44
He will enable us to stand in the last, most evil days.  Joel 228

In the NT:
God's preparation completed, Jesus was conceived by the Holy Spirit.  Math 118-21
      Their agreed plan of salvation for man from before the dawn of time!
Jesus reveals him as 'the Counsellor', when his own sacrificial work is 'finished':
      The gift of the Holy Spirit is promised.  Jn 1416,26 1526  167
      'He will teach you all things'.  Jn 1426
      'He will testify about me'.  Jn 1526
      'He will convict the world of guilt in regard to sin, righteousness
            and judgement'.  Jn 168
      'He will guide you into all truth'.  Jn 1613
      'The Spirit will take from what is mine and make it known to you'.  Jn 1615
      Named 'The Spirit of Truth', the One who reveals Jesus, the Word of God.
            Jn 1416,17 1526 1613-15  1Thes 15
      He enables us to 'hear' and understand; he brings faith and assurance.
      Prophetic truth is revealed - the now, and the yet to come. 
      He causes us to see our need and cry "What must I do to be saved?"  Act 237
The highlight of Pentecost is not wind, fire and tongues,
      but the souls of 3,000 earnest Jews who were saved!
      This is the evidence of the 'even greater things' that will be done because
            I am going to the Father and we will send the Spirit to you.  Jn 1412
Likewise, when the 72 returned to Jesus in triumph, Jesus said to them,
      "I saw Satan fall ... however, do not rejoice that the spirits are subject to you,
      but rejoice that your names are written in heaven."  Lu 1017-20
      Miracles reveal God's compassion and power.
            But his gracious plan is to rescue, to save, to redeem sinful, guilty men.
The Holy Spirit 'seals' us.  Our salvation in Christ is sure.  Eph 113,14 430
      Faith is more than hope; it is the revealed assurance of God.  Heb 111
      The Spirit guarantees our redemptive inheritance. His Word is true.
Sanctification is living practice of living by the Spirit.  Gal 516-26
      Jesus prayed, 'I have given them your word ... they are not of the world ...
      sanctify them by the truth; your word is truth.'  Jn 1714-17
He equips with power to preach repentance and forgiveness.  Lu 2429
      Disciples, filled with the Holy Spirit, spoke Word of God boldly.  Act 430
He transforms and renews our minds.  Ro 122 55  1Co 127-11
He enables men to discern will of God and guides in all matters, big and small.
Baptism of John and Baptism of Jesus.  Act 814-17 1824-26 191-7