How can you believe in someone you can't see?

Terry asked this question many times while I worked in The Nightshelter. He's mischievous, to say the least. And a charmer. He's the class-clown; the kid who always misbehaves in class but the teacher can't seem to punish because he flashes his dimples and dances his way out of trouble faster than you can say, "Terry, shut up and sit down!"
Even though Terry went to church every week, he claimed it was only because he wanted free doughnuts and coffee. He and his buddies mostly did just stand at the back of the room and scoff at everyone. He thought we Christians were weird and always tried to ruffle our feathers. I'll admit that even though I've been a Christian for most of my life and was fortunate enough to grow up in a Christian home, it was hard to answer some of his questions. It still is.
Perhaps one of my most memorable moments at the Nightshelter was halfway through my time there. I was starting a grilling 11 hour night shift and the middle lounge was full of residents. There were about five different conversations going on about the same subject: Is there a God, and if so, how can you believe and do what He says? I told Terry I know God exists because I've experienced Him. Of course Terry rolled his eyes and tried to discount my experience. So I tried a different approach: "I know God exists because if He didn't my brother would be crippled in a wheelchair, if not dead." Terry was unconvinced and explained that my brother was just lucky.
Even though Fiona, my co-worker, was involved in a conversation across the room, she jumped in and told Terry he couldn't say that because he hadn't even heard my testimony yet. Terry then turned to me and said, "Okay then, go on." I was stunned that he was willing to listen, so I quickly spoke up, lest he change his mind. A few seconds into my story, I was shocked to realize that the whole room was quiet and everyone was attentively listening to me.
I explained how my oldest brother, David, got very ill when he was nine. My parents took him to a doctor and eventually to a specialist because the docs believed he had juvenile rheumatoid arthritis. My mom took him to the appointment, and while he was being examined she sat in the waiting room that was full of parents and their sick children. She saw the kids at different stages of the disease, from relatively healthy-looking to those with shriveled-up arms and legs sitting in a wheelchair. Knowing that is what her son might face frightened her, so she moved to a different area and started praying. As she prayed, she randomly opened up her bible and immediately began reading a passage on healing. She prayed some more, turned to another part of the bible, and again her eyes fell on a passage about healing. She randomly flipped through her bible at least half a dozen more times and each time she read a story of healing. She knew in her heart that God was telling her He wanted to heal my brother. So when the doctor called her into the room and confirmed that David did have rheumatoid arthritis, she chose to believe what God spoke and not receive the doctor's words.
Mom and Dad continued to take David in for treatment, but they also gathered friends and family around to continuously pray. Days of prayer turned into weeks, and weeks turned into months. At some point, my parents did stop taking David to the doctor and chose to keep praying and walk out in faith. It was a long, grueling process, but when they all ran into David's doctor at the store nearly a year later, the doc was baffled when he saw my brother and claimed it was nothing short of a miracle; he exclaimed that David should have long been in a wheelchair.
When I finished my story, the guys were nearly speechless. So was I. I mean, what can you say when someone is diagnosed with a sickness and then later miraculously healed?
I share this story because I've recently been asked again about my faith - why and how can I believe in someone I can't see, especially when life sucks sometimes. I am blessed because faith comes easily for me and it has been rooted in me since I was a child. I can never stray far without being reminded of God's goodness. So in those dark moments, in those times I can't hear or feel or taste or see that God is there, I look behind me, at the path I've just traveled down; and I choose to believe that the past will carry me to the future, that the past is only a foretaste of what is to come.