I know many people have a picture of God in their minds, running all the way from a kindly old man (like your great-grandfather) to a stern policeman just waiting to punish them if they get out of line. And if we aren’t careful, we’ll end up making Him into someone just like us—which is idolatry.
But God is far greater than any of these! God does not have a physical body (which is why we shouldn’t reduce Him to a mere picture in our minds). He is a spiritual being who is infinitely glorious—all-powerful, all-knowing, all-wise, and all-loving. He also—unlike anyone you or I will ever know—is absolutely pure and perfect in all He does. The Psalmist put it this way: “As for God, his way is perfect: The Lord’s word is flawless; he shields all who take refuge in him” (Psalm 18:30).
You mentioned that you never knew your great-grandfather—but amazingly, you can know God! The reason is because some 2,000 years ago God stooped down from Heaven and became a man. That man was Jesus Christ, who was God in human flesh. The Bible says, “No one has ever seen God, but the one and only Son, who is himself God … has made him known” (John 1:18).
Why not put your faith and trust in Jesus Christ, and commit your life to Him? Then God will no longer be only a vague image in your mind, but He’ll become your closest friend—both now and forever.