The God & there is no God but He, Who has no partner, created us with a natural “fitrah.” I.e. belief in Him, but it is parents that change that to whatever it is they believe/don’t believe.
Then, later in life other things change that. But The God chooses to guide whom He Wills. And because He is guiding them, they don’t need to see to believe. His puts the belief, faith, love, fear, etc. for & of Him in their hearts.
He opens their eyes to His Creations that give them enough of a picture of His Greatness, that when they really see Him on The Day of Resurrection, it will be the greatest gift.
Example: please forgive me if you have read some of my previous answers/comments & know this already, but I love to quote it. Lets first read what The God says about Himself:
(The God is The Light of the heavens and the earth. The parable of His Light is as (if there were) a niche and within it a lamp, the lamp is in glass, the glass as it were a brilliant star, lit from a blessed tree, an olive, neither of the east (i.e. neither it gets sun-rays only in the morning) nor of the west (i.e. nor it gets sun-rays only in the afternoon, but it is exposed to the sun all day long), whose oil would almost glow forth (of itself), though no fire touched it. Light upon Light! The God guides to His Light whom He wills. And The God sets forth parables for mankind, and The God is All-Knower of everything.) (Quran 24:35)
2. (The God ! There is no god but He, The Ever Living, The One Who sustains and protects all that exists. Neither slumber, nor sleep overtake Him. To Him belongs whatever is in the heavens and whatever is on earth. Who is he that can intercede with Him except with His Permission? He knows what happens to them (His creatures) in this world, and what will happen to them in the Hereafter. And they will never compass anything of His Knowledge except that which He wills. His Throne extends over the heavens and the earth, and He feels no fatigue in guarding and preserving them. And He is The Most High, The Most Great.) (Quran 2:255)
3. (Say: He is The God , The One!The God , The Eternal, Absolute;”He begets not, nor was He begotten; And there is none like unto Him.) (Quran 112:1-4)
4. (No vision can grasp Him, but His Grasp is over all vision. He is The Most Subtle and Courteous, Well-Acquainted with all things.) (Quran 6:103)
I love painting a picture, but this one will make your brain bleed, lol.
He says His “Throne” extends over the heavens & the earth. We look like ants if one is looking down from a high enough building. We disappear from view if one looks down from a plane high enough. Everything disappears from view if one looks at the earth from the moon. The earth can fit 1000 times into Jupiter. And earth, the moon & Jupiter disappear from view the further into space one goes & looks back. That’s just in this galaxy. But there are galaxies within galaxies within galaxies. And His Tyrone “EXTENDS” over it all.
His Light, He gives an example of it. We can’t even look directly at the sun long enough without causing damage. So it is understandable that the mountain crumbled to dust when Moses asked to see Him:
(And when Moses came at the time and place appointed by Us, and his Lord spoke to him, he said: “O my Lord! Show me (Yourself), that I may look upon You.” The God said: “You cannot see Me, but look upon the mountain if it stands still in its place then you shall see Me.” So when his Lord appeared to the mountain, He made it collapse to dust, and Moses fell down unconscious. Then when he recovered his senses he said: “Glory be to You, I turn to You in repentance and I am the first of the believers.”) (Quran 7:143)
There is so much more in The Holy Quran & The Sunnah. The God completed The Religion of Prophet Abraham, sent His Last Prophet & Last Revelation. That is why it is so rich with information. Jesus said that the Comforter after him would guide us into all truths & we have more information about The God, His Prophets, His Revelations, & so much more. Because it is till The Day of Resurrection, so everything mankind will need is therein.