Here’s Alvin Plantinga on Calvin’s understanding of Holy Spirits ministry from an interview on his relationship to Barth;

Moore: Calvin’s understanding of the internal witness of the Spirit looms large for you. Would you give us a brief definition of what the internal witness of the Spirit meant for Calvin, and how it has influenced your own understanding of the Christian life?

Plantinga: As I understand Calvin, he follows St. Paul in holding that the Holy Spirit confirms the message of the gospel to our hearts and minds. In this way God announces the good news to us human beings, and then also enables us to, helps us to, accept and believe it. I believe that Calvin is right on this point, and that the witness of the Holy Spirit, even though it can be muffled and distorted by our sin, is essential to the Christian life.

Read more over at Jesus Creed