We think that when we fail to trust God in our daily situations, we only harm ourselves. We think we’re simply missing out on His blessings. But that isn’t the whole story. First of all, we hurt and anger our blessed Lord. He warns, “If you don’t trust Me, you’re going to develop a hardened heart.”

We read in Hebrews: “Harden not your hearts, as in the provocation, in the day of temptation in the wilderness: when your fathers tempted me, proved me, and saw my works forty years. Wherefore I was grieved with that generation, and said, They do always err in their heart; and they have not known my ways. So I sware in my wrath, They shall not enter into my rest” (Hebrews 3:8-11).

What reason is given for God’s people being unable to enter into His rest? Was it because of adultery, covetousness, drunkenness? No, it was because of unbelief alone. Here was a nation exposed to forty years of miracles, supernatural wonders that God worked on their behalf. No other people on earth had been so loved, so tenderly cared for. They received revelation after revelation of the goodness and severity of the Lord. They heard a fresh word preached regularly from Moses, their prophet leader.

But they never mixed that word with faith. Therefore, hearing it did them no good. In the midst of all those blessings, they still didn’t trust God to be faithful. And over time, unbelief set in. From that point on, darkness covered their wilderness journey.

Unbelief is the root cause behind all hardness of heart. Hebrews asks, “With whom was he grieved forty years? Was it not with them that had sinned, whose carcases fell in the wilderness?” (3:17). The Greek word for grieved here signifies indignation, outrage, anger. Simply put, the people’s unbelief kindled God’s anger against them. Moreover, it hardened them into a continual spiral of unbelief: “Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God . . . lest any of you be hardened through the deceitfulness of sin” (3:12-13). 

Unbelief is the mother of all sins. It was the first sin committed in the Garden of Eden and it’s at the root of all bitterness, rebellion and coldness. That’s why Hebrews 3 is addressed to believers (“Take heed, brethren”). The writer concludes with these chilling words: “To whom sware he that they should not enter into his rest, but to them that believed not? So we see that they could not enter in because of unbelief” (3:18-19).