Luke 16:10

He who is faithful in a very little thing is also faithful in much; and he who is dishonest in a very little thing is also dishonest in much.  

Our integrity matters and shows whether we can be relied on by God. Suppose we are not faithful and reliable in the little things. God will never let us handle the challenge of something larger. We would not be trustworthy and would fail. A greater reward exists for being faithful in very little because it will lead to us being able to be faithful in much.