The Israelites would not use their faith; they would not step out. They held back because the bottom line was that they did not really believe it.
Do we believe what we are hearing from the Word of God? If we do not believe it, we will do nothing. We only do what we believe.
Everybody in the world operates by this principle—they do what they believe! But do they believe God? No. We are in God's church because we believe, and because we believe in the right way, we obey God. In Hebrews 3, Paul equates "belief" and "obedience." It makes for an interesting study. Despite being significantly different, the effect of one should be the product of the other.
This is why one can find words like "belief" or "unbelief" in Scripture, and see in the margin that "obedience" or "disobedience" can be an alternate translation. The words can be taken either way.
We do what we believe. The real problem is becoming apparent. The reason the Hebrews were apathetic—the reason they were neglecting their spiritual priorities—was because their belief system had undergone a serious change since the time that they had first heard.
When Satan wants to divide or destroy a church, he often does so through inspiring changes in the doctrines. When the doctrines change, the belief system changes accordingly. And when the belief system changes, those who believe the same basic way will flock together, and those who believe a different way will coalesce into another group.
When a belief changes, a change in conduct must follow. This is what happened to the Israelites in the wilderness. They did not believe God, and they failed. They all died. That whole first generation died as a result of their disbelief.