For the cloud of the LORD was on the tabernacle by day, and fire was in it by night, in the sight of all the house of Israel throughout all their journeys. (Shemot / Exodus 40:38; ESV)
The Torah teaches us two essential factors about the nature of God. First, God is non-material. He is not made up of the stuff of creation. This is one reason why he is not to be represented by idols. Man's greatest attempt to represent God through man-made items is futile, for his fullness cannot be comprehended by our physical senses.
The second essential factor is that while God himself is immaterial, he makes himself known within the material world he has made. Even though he is unseen, what he does is clearly seen. The creation is prime evidence for his existence. The design of the universe from the smallest particle to the vastness of space shouts to us of the reality of the Designer. More than that, God also makes himself known through unusual acts of power. God's deliverance of Israel from oppression in Egypt is an example of this. The ten plagues were not natural disasters. They were intended by God to show to Israel, Egypt, and the world how powerful he was and where his allegiance lay.
During the 40 years of Israel's wilderness wanderings, God also showed himself through various miracles of protection, provision, and punishment. Israel was to learn that God was not just a concept or a power to manipulate. Though he himself could not be seen and no image could be concocted that could adequately represent him, he was very real.
Another way God communicated himself was through a cloud that stayed with them during their wilderness years. The cloud protected them and guided them in their journeys. The cloud itself wasn't God. They didn't worship the cloud. Yet the cloud was a visible representation of his presence.
How wonderful it would be to have such a visible representation of God's reality and presence with us today! How certain we would be of God's existence, love, and leading! But then again, would we? The visibility of God didn't actually make a difference to the majority within the nation of Israel. All the adults who were miraculously delivered from Egypt were judged by God for their unfaithfulness and died before ever entering the Promised Land. All these visible manifestations of God's reality made no difference in their lives.
The people's lack of faithfulness to God in no way diminishes the reality of God's visibility. This lack only testifies to the depth of human beings' alienation from God. For those who were faithful to God, his visibility was a great comfort and help. God's visibility doesn't produce right relationship with him. But for those who truly trust him, the various ways God makes himself known, make an enormous difference.
This is not to say that knowing God is a personal, subjective experience as if the visibility of God is dependent on faith. Just like the whole nation of Israel saw the cloud and was benefited by it, God makes himself known to all people in a variety of ways. The difference that trusting him makes has to do with the effect of his visibility on us. When we are in right relationship with him, then the ways he reveals himself enhances that relationship.