Hebrews 3:10

“Wherefore I was severely displeased with this generation, And said, They do always err in their heart, but they did not know my ways.”

As a result of their murmuring and their provocation of God, God’s severe displeasure came on that whole generation, because, as He said, ‘they erred in their hearts and did not know His ways’. First their hearts were wrong, and then it resulted in wrong behaviour. The inference is that his readers must beware lest the same thing be true of them. Note those two downward steps. First their hearts went astray, and that was followed by a failure to acknowledge His ways. Unbelief results from a straying heart not a doubting mind, the doubting mind follows to make it respectable. By ‘the heart’ is meant spiritual and moral responsiveness from within, from what a man essentially is, and includes both mind and emotion. As a man thinks in his heart, so is he.