The sin of unbelief

See to it, brothers, that none of you has a sinful, unbelieving heart that turns away from the living God. But encourage one another daily, as long as it is called Today, so that none of you may be hardened by sin's deceitfulness. (Heb 3:12-13)

So, as the Holy Spirit says: "Today, if you hear His voice, do not harden your hearts as you did in the rebellion, during the time of testing in the desert, where your fathers tested and tried Me and for forty years saw what I did. That is why I was angry with that generation, and I said, Their hearts are always going astray, and they have not known My ways. So I declared on oath in My anger, They shall never enter My rest." (Heb 3:7-11) God's ways is God's rest, is resting in the finished work of His Son. See to it that you do not fall like your fathers in the wilderness, not enter into His rest because of their unbelief. Behold unto Jesus for He is the way, He is the rest. Hear Him!