Institutes of the Christian Religion (1559) - John Calvin
Book 3 - How We Receive the Grace of Christ
Chapter 3 - Our Regeneration by Faith: Repentance
Sections 16-20 - Fruit of repentance - lifelong holiness, confession
Section 16 - Outward and inward repentance
We have to measure ourselves by God's law to be sure of our repentance.
"When we have to deal with God nothing is achieved unless we begin from the inner disposition of the heart."
Joel 2:13; James 4:8.
Outward, bodily denial and disciplines to express repentance are okay, but tend to obscure the spiritual emphasis.
Section 17 - The outward practice of penance must not become the chief thing
It is fine for pastors to call their churches to fasting, provided they emphasize the rending of hearts more - Matt 9:15; Joel 2:13.