Here’s a great question to use at a candidate’s ordination exam for the ministry in the PCA:

“Do you believe that Christians can willfully render useless the grace of God by which they have been joined to Christ by the Spirit and made recipients of the blessings of adoption and regeneration?” 

Here is John Calvin’s answer from his commentary on Hebrews 10:29:

The Spirit of grace. He calls it the Spirit of grace from the effects produced; for it is by the Spirit and through his influence that we receive the grace offered to us in Christ. For he it is who enlightens our minds by faith, who seals the adoption of God on our hearts, who regenerates us unto newness of life, who grafts us into the body of Christ, that he may live in us and we in him. He is therefore rightly called the Spirit of grace, by whom Christ becomes ours with all his blessings. But to do despite to him, or to treat him with scorn, by whom we are endowed with so many benefits, is an impiety extremely wicked. Hence learn that all who willfully render useless his grace, by which they had been favored, act disdainfully towards the Spirit of God. It is therefore no wonder that God so severely visits blasphemies of this kind; it is no wonder that he shows himself inexorable towards those who tread under foot Christ the Mediator, who alone reconciles us to himself; it is no wonder that he closes up the way of salvation against those who spurn the Holy Spirit, the only true guide.

Here are a list of quotations by John Calvin.  If you are already acquainted with some of them, I think the odds are good you heard about them through the renaissance in appreciation of our Reformed heritage which commonly goes by the name, “Federal Vision.”