A new heart from heaven

8. Then follows, Harden not your hearts By which words is intimated that our rebellion against God flows from no other fountain than willful wickedness, by which we obstruct the entrance of his grace, We have indeed by nature a heart of stone, and there is in all an innate hardness from the womb, which God alone can mollify and amend. That we, however, reject the voice of God, it happens through a spontaneous obstinacy, not through an external impulse, a fact of which every one is a witness to himself. Rightly, then, does the Spirit accuse all the unbelieving that they resist God, and that they are the teachers and authors of their own perverseness, so that they can throw the blame on none else. It is hence, however, absurdly concluded that we have, on the other hand, a free power to form the heart for God’s service; nay rather, it must ever be the case with men, that they harden their heart until another be given them from heaven; for as we are bent towards wickedness, we shall never cease to resist God until we shall be tamed and subdued by his hand.

 - John Calvin on Hebrews 3:8