You do not know, but you believe. That is what faith is. But faith is not automatic; faith is a gift. What does that mean?
Think of when you receive a gift that you’re not quite sure of, but you love the one who gave you the gift. Would you throw it away, or would you set it on the table? Each time you walk by it, you look at it, twist your face a little, and think about throwing it away. But you don’t, because it reminds you of the one you love. So you keep it. For years and years you keep it, if only because it reminds you of the one you love.
Then one day when you are out walking on the street, you see the very same item in a shop window. It reminds you of the one you love so strongly that you have to go into the shop and see why it’s there, and how they got it. Turns out, it’s not for sale. It’s just there because the shop owner wants to show it to the world, which so badly needs this gift.
And maybe your doubt gives it the greatest meaning of all.