“They did not believe His word, But complained in their tents, And did not heed the voice of the Lord” (Psalm 106:24-25 NKJV)

It wasn’t external enemies that kept the Israelites out of the Promised Land. It was their internal grumbling. They complained against the food and against their leaders, but really they complained against God. So He allowed the grumblers to die in the wilderness, while raising up a new generation that believed. Complaining is the opposite of gratitude. It is the opposite of worship. It doubts God’s provision and Word.