I believe in Abraham Lincoln. I'm reading a book about him. I can go to historic sites and see details of his life explained to me. There are a number of histories that have record of him. His face even shows up on money. Though he lived many years before me, I believe that he existed, was our 16th President, and that he was a good man. That's one example of belief.
I am also believing in this chair that I am sitting in as I type these thoughts. (Were you to see this chair and know my size, you'd consider this an act of great faith!) You see, I am resting my weight upon this chair depending upon it to do what it promises to do - namely hold me up. If it fails to do what it is promised to do I will fall. This is another example of belief.
The world is full of people who believe in Jesus by that first definition - Jesus is a historical figure that lived a long time before us; he was a good moral teacher; he was a gentle and kind man; and so on. But the Biblical definition of believe, the one that John speaks of 98 times, is one of placing your faith in Jesus to do exactly what He said He would do - bring you into a relationship with your God. It means you're resting upon Him, and Him alone for salvation. It means you trust in Him to the degree of resting your eternal hopes on Him. And again, that verse, John 3:18, suggests that you are either on one side of that Biblical definition of believe or the other. So how do you define 'believe'?