John Calvin Commentary Hebrews 3:8

"Harden not your hearts, as in the provocation, Like as in the day of the trial in the wilderness," — Hebrews 3:8 (ASV)

Then follows, Harden not your hearts. These words intimate that our rebellion against God flows from no other fountain than willful wickedness, by which we obstruct the entrance of His grace. We indeed have by nature a heart of stone, and there is in all an innate hardness from the womb, which God alone can soften and change.

That we reject God's voice, however, happens through spontaneous obstinacy, not through an external impulse—a fact to which each person is a witness in himself. Rightly, then, does the Spirit accuse all unbelievers that they resist God, and that they are the teachers and authors of their own perverseness, so that they can blame no one else.

From this, however, it is absurdly concluded that we, on the other hand, have free power to form our hearts for God’s service. No, rather, it must always be the case with people that they harden their hearts until another heart is given to them from heaven. For as we are inclined towards wickedness, we will never cease to resist God until we are tamed and subdued by His hand.

As in the provocation, etc. It was necessary for them to be reminded of the disobedience of their fathers for two reasons: since they were foolishly puffed up because of the glory of their race, they often imitated the vices of their fathers as though they were virtues and defended themselves by their examples; and further, when they heard that their fathers had been so disobedient to God, they were thus more fully taught that this admonition was not superfluous. Since both these reasons existed even in the Apostle’s time, he readily adapted for his own purpose what David had formerly said, so that those whom he addressed might not imitate their fathers too much.

And from this a general truth may be learned: that we should not defer too much to the authority of the fathers, lest it draw us away from God. For if any fathers have ever been worthy of honor, no doubt the Jewish fathers possessed that preeminence; and yet David distinctly commanded their children to beware of being like them.

And I have no doubt that he referred to the history recorded in Exodus 17, for David uses here the two names that Moses relates were given to a certain place: Meribah (מרבה), which means strife or provocation, and Massah (מסה), which means temptation. They tempted God by denying that He was in their midst because they were distressed for want of water, and they also provoked Him by contending with Moses.

Though they indeed gave many examples of unbelief, David selected this one in a special manner because it was more memorable than any other, and also because, in order of time, it mostly followed the others, as is evident from Numbers, where chapters 10–20 describe a series of many temptations, while this particular narrative is given in Numbers 20. This circumstance considerably increased the atrocity of their wickedness, for they had often experienced the power of God, and yet they perversely contended with Him and renounced all confidence in Him. How great was their ingratitude! He then mentioned one particular instance instead of many.