they say, "to see is to believe," but how could you say that you believe if you already see it? 
The essence of believing is when you put your faith and trust to what is unseen, not to what is already seen. 
God has given us the capacity to believe into something that we cannot see - that's faith, and trusting Him. 


I say, "I believe in God," but I do not see Him. well, that's faith and trust in Him.