'Harden Your Hearts' in the Bible

do not harden your hearts as in the rebellion, on the day of testing in the wilderness,

while it is said, "Today, if you will hear his voice, do not harden your hearts as in the rebellion."

God again set a certain day, "Today," saying through David after so long a time just as has been said before, "Today, if you hear his voice, do not harden your hearts."