“As it is said: Today, if you hear His voice, do not harden your hearts as in the rebellion. For who heard and rebelled? Wasn’t it really all who came out of Egypt under Moses? And who was He provoked with for 40 years? Was it not with those who sinned, whose bodies fell in the wilderness? And who did He swear to that they would not enter His rest, if not those who disobeyed? So we see that they were unable to enter because of unbelief.”
Hebrews 3:15-19 HCSB
The author of Hebrews is obviously speaking to the Hebrews, and so he is tying the acts and words from the Old Testament to what is needed today. I like this analogy because he points out that unbelief is what will separate is from God.