Hebrews 3

A Warning To Our Hearts

Therefore, as the Holy Spirit says, "Today, if you hear his voice, do not harden your hearts as in the rebellion, on the day of testing in the wilderness, where your fathers put me to the test and saw my works for forty years. Therefore I was provoked with that generation, and said, 'They always go astray in their heart; they have not known my ways'. As I swore in my wrath, 'They shall not enter my rest.'" – Hebrews 3:7-11

Our sinful tendency is to harden our hearts and rebel against God. This causes us to go astray in our ways, and our hearts will not know God's ways.

Take care, brothers, lest there be in any of you an evil, unbelieving heart, leading you to fall away from the living God. – Hebrews 3:12

For extra emphasis, we are told to be cautious about our hearts, especially because its inherent sinful nature is to be evil and unbelieving in truth.