Why is it so hard for Christians to believe God?

Then they told him, and said: "We went to the land where you sent us. It truly flows with milk and honey, and this is its fruit. 28 Nevertheless the people who dwell in the land are strong; the cities are fortified and very large; moreover we saw the descendants of Anak there. - Numbers 13:27-28

When the spies came back from Canaan, only Caleb and Joshua believed God and told the children of Israel they were more than able to take the land for God was with them. The other ten gave them a very negative report that there were giants in the land and that they were like grasshoppers compared with them. The other ten simple just didn't believe God was good and as a result of their unbelief they would not enter the promised land.

The twelve spies obviously spied out the same promised land which the God has given to them. Yet only Caleb and Joshua believed God and gave the children of Israel a good report. Why the disparity of views?

I believe Caleb and Joshua had a very good opinion of God and they put their trust in God and that God will bring them into the promised land in spite of the giants in the land. They simply believed the word that God has spoken to them. They put their trust in God!

The other ten spies looked at their own "weakness" instead on looking unto God who had delivered them from Eqypt. They focused on their small-ness instead of the largeness of God. They put their trust in their own "dis"-abilities instead of God infinite ability. They simply look to themselves for help instead of resting in the love of God for them.

What happened then is a lesson for us to learn. We are not to look at ourselves for our own providence for there is nothing good coming out of one's own strength. We are not to focus on our challenges and problems but look to the Lord who is more than willing to deliver us out of our predications. He is a loving God who never fails. His timing is always perfect. Our every battle belongs to the Lord!

The moment we look to our own strength to overcome the negative circumstances, it will never produce good result. And it will cause us to be stressed out and burnt out and fall into self-condemnation. Also, somethings we become proud and forget the presence of the Lord. Sometimes we even forget our own identity in Christ! 

Therefore, we are to look to Jesus for our every need. Look at His grace towards us. Focus on His love for us and personalize that love so much that it becomes very real in our lives. Cultivate the presence of the Lord constantly. Commune with Him regularly for He loves to commune with us. Listen to His word. Read His word. It is easy to believe God when we are full of Jesus in our lives. Keep building on that faith and we shall find believing in God becomes second nature.