Deuteronomy 1:34-39 “And the LORD heard your words and was angered, and he swore, ‘Not one of these men of this evil generation shall see the good land that I swore to give to your fathers, except Caleb the son of Jephunneh. He shall see it, and to him and to his children I will give the land on which he has trodden, because he has wholly followed the LORD!’ Even with me the LORD was angry on your account and said, ‘You also shall not go in there. Joshua the son of Nun, who stands before you, he shall enter. Encourage him, for he shall cause Israel to inherit it. And as for your little ones, who you said would become a prey, and your children, who today have no knowledge of good or evil, they shall go in there. And to them I will give it, and they shall possess it.
In response to Israel’s unbelief and lack of trust in God’s love, God swore an oath (Psalm 95:11) that the adult generation which came out of Egypt would not inherit the Promised Land, but would die in the desolate wilderness instead. The only exceptions were Caleb and Joshua. These were the faithful two among the twelve spies which came back with the report from the Promised Land. Even Moses himself would not enter the Promised Land. (Guzik)
And the Lord heard the voice of your words,…. Of their murmurings against Moses and Aaron, and of their threatenings to them, Joshua and Caleb, and of their impious charge of hatred of them to God for bringing them out of Egypt, and of their rash wishes that they had died there or in the wilderness, and of their wicked scheme and proposal to make them a captain, and return to Egypt again: (Gill)
Doubts form out of lack of trust and reliance in God and lead to disobedience. Knowing God and having an ever-growing desire to know more and more of Him will give us confidence in His power and sovereignty over all things on earth and in heaven. I dare say that lack of desire for His Word and knowing Him more and more leaves a void that will be filled with foolish thoughts, doubts, fear, anger, worry, confusion, etc…. His Word is given to us so that we have examples of His awesome power, might, and control over all things. It also gives us examples of His grace, mercy, and love, as well as, right and wrong thinking which led to distrust, disregard, and denial of His power, promises, purpose, and plans.