This assumes that having as many people believe as possible is God's design. Sure, God could rip open the very fabric of physical reality and descend from heaven with legions of angels at His side and tell us His will. That would almost certainly bring all but the most determined (to the point of being deranged) non-believer to belief. But for God to impose Himself so directly would probably be catastrophic for the flow of human history. At the very least it would force us to faith when the Gospel is meant to be an offer. Faith itself is a gift, not an imposition.Why does God need books (or other written text) to spread his word? Seems like an incredibly inefficient means for an all powerful being. Surely an all wise and all powerful God could have come up with something better. I mean such things as sacred text and oral tradition, that is so crude and clumsy it seems more like something people would come up with.
My faith teaches that the knowledge of God is implanted within the human soul. God isn't hidden for those who genuinely want to find Him. But it takes humility and a lot of prayer.