"The Reformers on the Necessity for Repentance and Sanctification"

                  John Calvin:

Even though we have taught in part how to possess Christ, and how through it we enjoy his benefits, this would still remain obscure if we did not add an explanation of the effects we feel. With good reason, the sum of the gospel is held to consist in repentance and the forgiveness of sins (Luke 24:47; Acts 5:31). Any discussion of faith, therefore, that omitted these two topics would be barren and mutilated and well–nigh useless...Surely no one can embrace the grace of the gospel without betaking himself from the errors of his past life into the right way, and applying his whole effort to the practice of repentance.
Can true repentance stand apart from faith? Not at all. But even though they cannot be separated, they ought to be distinguished (Institutes of the Christian Religion. Found in The Library of Christian Classics (Philadelphia: Westminster, 1960), Volume XIX, Book III, Chapters 1, 5, pp. 592-593, 597).

The Hebrew word for ‘repentance’ is derived from conversion or return; the Greek word, from change of mind or of intention. And the thing itself corresponds closely to the etymology of both words. The meaning is that, departing from ourselves, we turn to God, and having taken off our former mind, we put on a new. On this account, in my judgment, repentance can thus be well defined: it is the turning of our life to God...When we call it a ‘turning of life to God,’ we require a transformation, not only in outward works, but in the soul itself. Only when it puts off its old nature does it bring forth the fruits of works in harmony with its renewal. The prophet, wishing to express this change, bids whom he calls to repentance to get themselves a new heart (Ezek. 18:31).
Outward uprightness of life is not the chief point of repentance, for God looks into men’s hearts. Whoever is moderately versed in Scripture will understand by himself...that when we have to deal with God nothing is achieved unless we begin from the inner disposition of the heart (emphasis mine). (Institutes of the Christian Religion. Found in The Library of Christian Classics (Philadelphia: Westminster, 1960), Volume XIX, Book III.3. 5-6, 16, pp. 597-598, 609-610.