He (God) took him (Abram/Abraham) outside and said: “Look up at the sky and count the stars, if you can. Just so,” he added, “shall your descendants be.” Abram put his faith in the LORD, who credited it to him as an act of righteousness. Genesis 15:5-6
Most people envision Abraham looking up at a night sky full of stars. However, a few verses later, the story continues.
As the sun was about to set, a trance fell upon Abram/Abraham … Gen 15:12
So envision Abraham looking up at a bright blue sky and having faith that his children would be beyond numbering, just as the stars he could not see at the moment were beyond numbering. Abraham could not see the stars, but believed the stars were still there.
St Paul wrote that ” faith is belief in things not seen”. Please let me restate that: faith is belief based on rational thought applied to observations of reality. We exercise faith all the time: faith that gravity will keep working; faith that the sun will keep shining; faith that water will boil if heated enough. Faith in God can come from the same process of rational thought applied to observations of reality.
Remember how Jesus said to him (John), “… Blessed are those who have not seen and have believed.” John 20: 29
If Jesus gave us absolute proof of His existence, He would leave us no choice but to believe. By giving us great evidence, but not absolute proof, Jesus allows us to choose be rational and believe rather than be emotional and dis-believe.