We believe that when we fail to trust God in our everyday situations, we do harm to ourselves. We think we're missing just blessings. But that's not all. First, we hurt and get angry our Lord. He warns: "If you do not trust me, you will develop a hardened heart."
We read in Hebrews: "Harden not your hearts as in the rebellion, in the day of temptation in the wilderness, where your fathers tempted me, proved me, and saw my works forty years. Wherefore I was grieved against this generation, and I said: They always have a heart that wanders. They have not known my ways. So I swore in my wrath, if they shall enter into my rest "(Hebrews 3: 8-11)!.
What reason is given for the inability of the people of God to enter into His rest? Was it because of adultery, lust, drunkenness? No, it was solely because of their unbelief. Here we see a nation exposed to miracles and supernatural wonders that God has done for them for forty years. No other people on earth has been as loved as well supported. They received revelation after revelation of the goodness and severity of God. They heard a fresh word preached regularly be them from Moses, their leader and prophet.
But they never received the word by faith. Therefore the fact of hearing them was not good. Amidst all these blessings, they still did not fully trust God. And, over time, unbelief set in. From that moment, the darkness covered their wilderness journey.
Unbelief is the root behind all hardness of heart. The Epistle to the Hebrews asks, "And against whom was he grieved forty years, if not against those who sinned, whose bodies fell in the wilderness?" (3:17). The Greek word used here means pained angry, indignant, outraged, bitter. To put it simply, the unbelief of the people lit the wrath of God against them. Moreover, it leads them into a continuous spiral of hardness and unbelief: "Take heed, brethren, in any of you an evil, unbelieving heart that turns away from the living God .. .To that none of you may be hardened by 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 this is the root of all bitterness, rebellion and cooling of the heart. It is for this reason that Chapter 3 of the book of Hebrews is addressed to believers ("Take heed, brethren"). The author concludes with these chilling words: "And to whom did he swear 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).