Does God exist? If so, what's He like? Jesus Christ claimed to be God's Son come to earth. If true, by observing Him we can get to know God. That's why John wrote this book. For three years Jesus was teaching, hanging out and doing miracles to back up His radical claims.
Strangely and sadly, millions have opted not to become associated with Jesus. It seems that hearing about Him, even seeing Him is not enough. Jesus says those who come to a personal faith in Him have been drawn by His Father.