First of all, this is a very good question that is asked. The Bible says blessed are those that believe but have never see. I believe in Him because over 2000 years ago He died for me on an old rugged cross which was an emblem of suffering and shame.
The pessimist, the antagonist, th negative folk will have you to believe that nothing is sure, nothing is certain, and that nothing is forever.
But I beg to differ with these spitually absentminded folk because Jesus is sure....HE's for certain... and yes He's forver. He's my assurance....my Blessed Assurance. You know what my friend, Jesus loved me and still loves me despite the fact that I sometimes sin.
I believe in Him because of my personal experience that I have had and I still have with Him. Paul had his experience with Jesus on the Damascus Road. My experience may not have been like Paul's experience but never the less I've had my own experience. Yes He walks with me and He talks with me. I know who I am and I know whose I am. There's not enogh room or time for me to tell why I believe in HIm. He is Real, Yes He's real and I can feel Him in my soul!