Psalm 95:8

Psalm 95:7-11 (see also Isaiah 65:2Jeremiah 18:13)
For He is our God, and we are the people of His pasture and the sheep of His hand. Today, if you would hear His voice, do not harden your hearts, as at Meribah, as in the day of Massah in the wilderness, “When your fathers tested Me, They tried Me, though they had seen My work. For forty years I loathed that generation, and said they are a people who err in their heart, and they do not know My ways.  Therefore I swore in My anger, Truly they shall not enter into My rest.”

Moses called the place Massah (testing) and Meribah (rebellion).

​Question: Is the point of this, that they had no control over the condition of their hearts?

Answer: That would be a rather odd conclusion. This is similar to Isaiah 65:2, which indicates that God had reached out to His people, all day long, but who had refused Him. Add to that, Jeremiah 18:1-13, in which God had implored Israel to turn back to Him, in which Israel responded that it could not (which God felt was a would-not, rather than a could-not). God, in turn, appealed to the heathen nations, whether they had ever heard of anything so absurd. The only reasonable conclusion, then, is that they did have some form of control over the condition of their hearts, since God made it so, and hence Israel is accountable for how they used that freedom and opportunity.