The matter of fact is the emphasis on 'unseen'..now how the hell do u prove unseen?
why is that difficult? that you see is the 'seen' and that you don't see is the unseen.
A judge never sees a crime but is able to judge on it through rules of evidence and procedure. Here the crime is unseen to him but yet with proper stems he is convinced by the prosecutor that teh crime 'existed' ie happened or was committed.
You can ofcourse understand 'unseen' as either literally associated with the one sense (sight) or encompassing all senses (smell, touch, hearing etc).
That's why I said a long time ago - the best proof of God to any individual, including those who don't believe in God, is their own thought. They can have a thought but cannot prove to anyone else that they had that thought except circumstantially.