John Calvin Commentary Hebrews 4:7

"he again defineth a certain day, To-day, saying in David so long a time afterward (even as hath been said before), To-day if ye shall hear his voice, Harden not your hearts." — Hebrews 4:7 (ASV)

However, there is some more difficulty in what he immediately adds: that another today is appointed for us in the Psalm because the former people had been excluded. But David's words, one might say, seem to express no such thing and mean only this: that God punished the people's unbelief by refusing them possession of the land.

To this I answer that the inference is correct: what was denied to them is offered to us. For the Holy Spirit reminds and warns us not to do the same thing, lest we incur the same punishment. For how does the matter stand? If nothing were promised today, how could this warning be suitable: Take heed lest the same thing happen to you as to the fathers. Therefore, the Apostle rightly says that just as the fathers’ unbelief deprived them of the promised possession, the promise is renewed to their children, so that they may possess what their fathers had neglected.