Degrees of Faith
Words can have different meanings. To 'know' someone, for example, can mean "to simply be familiar" with someone or it can mean "to have a close relationship" with them and everything in between. The same gamut can be seen in a word like 'belief' and 'faith.' All the spies had belief and faith in God — meaning they were confident of His existence. But only two spies had a belief and faith that took them to the next level — to trust in Him and to obey Him. God asked the question, "how long will they refuse to believe in me, in spite of all the signs I have performed among them?" to Moses in Numbers 14:11. God was asking when their faith and belief were going to step up to the next level in a sense. He knew they believed in His existence, but they had yet to believe that He could do things and save them from any situation He wanted. However, Joshua and Caleb's faith was already at that level — they were ready to go and conquer the land knowing God was with them. Their faith was pushing them to act. James makes this point in James 2:17 when he says that faith without action (i.e., works) is dead; what good is it? What good is it to know God is present, but not know He will take care of His people? All the spies had some faith in God, but not all of them had the degree of faith God required. The same went for the Israelites for a while … time and time again in their history they lacked the faith they needed.
Excerpt from Moses and Old Testament Law