Numbers 13

Moroni taught -

"...if there be no faith among the children of men God can do no miracle among them..." (Book of Mormon | Ether 12:12)

Nephi said to his bothers -

"...how is it that ye have forgotten that the Lord is able to do all things according to his will, for the children of men, if it so be that they exercise faith in him?" (Book of Mormon | 1 Nephi 7:12)

It is any wonder why the Lord would seem so frustrated when the spies sent by Moses returned to report -

"...We be not able to go up against the people; for they are stronger than we." (Old Testament | Numbers 13:31)

It was only Joshua and Caleb that demonstrated faith saying -

"...Let us go up at once, and possess it; for we are well able to overcome it..." (Old Testament | Numbers 13:30)

As the people murmured, siding with ten of the spies, the Lord explained what he was going to do and why -

"Because all those men which have seen my glory, and my miracles, which I did in Egypt and in the wilderness, and have tempted me now these ten times, and have not hearkened to my voice;
23 Surely they shall not see the land which I sware unto their fathers, neither shall any of them that provoked me see it..." (Old Testament | Numbers 14:22 - 23)

And even their -

"...children shall wander in the wilderness forty years, and bear your whoredoms, until your carcases be wasted in the wilderness.
34 After the number of the days in which ye searched the land, even forty days, each day for a year, shall ye bear your iniquities, even forty years, and ye shall know my breach of promise." (Old Testament | Numbers 14:33 - 34)

The Lord desired to bring these people into the promised land, but He could not because of their lack of faith. It would take forty years to develop the faith required to overthrow the wicked people of the land.