The vision of God
From the book: The Genesis – Allan Kardec

If God is everywhere, why don't we see him? Will we see him after we leave the earth? These are the questions we are asked every day.
The first can be easily answered. Our material organs have limited perceptions which do not allow them to see certain things, even material things. Thus, certain fluids totally escape our vision, as well as our instruments of analysis, although this does not give us any reason to doubt their existence. We see the effects of plague, but we do not see the fluid that transmits it; we see bodies in motion under the influence of the force of gravity, but we do not see that force.
Material organs cannot perceive things of spiritual essence. We can only see the Spirits and things of the immaterial world with the vision of the Spirit. Therefore, only our soul can have the perception of God. Will it see Him immediately after death? In this respect, only the communications from beyond the grave can enlighten us. Through them we come to know that the vision of God is the exclusive privilege of the most purified souls, and that very few, when they leave the earthly sheath, possess the degree of dematerialisation necessary for it. A vulgar comparison will make this easy to understand.
A person standing at the bottom of a valley, shrouded in a dense mist, cannot see the sun. However, through the diffuse light he perceives that the sun is shining. If he decides to climb the mountain, as he ascends, the haze will dissipate more and more and the light will become more and more vivid. However, you will not yet see the sun. It is only after you have risen completely above the layer of mist, and have reached the point where the air is perfectly clear, that you will behold the sun in all its splendour.
The same is true of the soul. The perispiritual sheath, though invisible and intangible to us, is in relation to the soul a real matter, still too gross for certain perceptions. That sheath becomes spiritualised as the soul rises in morality. The imperfections of the soul are like misty layers that cloud the vision. Each imperfection it sheds is one less blemish, but it is only after it has been fully purified that it enjoys the fullness of its faculties.
Since God is the divine essence par excellence, He can only be perceived in all His splendour by spirits who have attained the highest degree of dematerialisation. As for the imperfect spirits, it does not follow from the fact that they do not see God that they are more distant from Him than others, for, like all beings in nature, they are immersed in the divine fluid, just as we are immersed in light. What happens is that the imperfections of these spirits are like vapours which prevent them from seeing Him. When the mist dissipates, they will see it resplendent. For that they need not ascend or seek it in the depths of the infinite. When their spiritual vision is unobstructed from the moral stains which obscured it, they will see Him, wherever they are, even on earth, for God is everywhere.
The spirit purifies himself in the course of time, and the different incarnations are stills in the bottom of which he leaves some impurities each time. Spirits, on leaving their corporeal envelope, do not instantly divest themselves of their imperfections, which is why, after death, they do not see God any more than they did when they were alive. However, as they purify themselves, they have a clearer intuition of Him. Even if they do not see Him, they understand Him better, for the light is less diffused. So when some spirits say that God forbids them to answer a question, it does not mean that God has appeared to them or spoken to them to command or forbid them to do this or that. Of course not. They feel it, they receive the effluvia of his thought, just as we do in relation to the spirits who envelop us in their fluids, though we do not see them.
No man can, therefore, see God with the eyes of the flesh. If such a grace were granted to some, it would only be realised in a state of ecstasy, when the soul is so detached from the bonds of matter as to make it possible during the incarnation. On the other hand, such a privilege would belong exclusively to select souls, who have incarnated in fulfilment of some mission, and not to those who have incarnated in order to atone for their sins. However, since spirits of the highest rank shine with dazzling brilliance, it may happen that lesser spirits, whether incarnated or disincarnated, marvelling at the splendour which surrounds them, may suppose that they see God Himself. It would be like one who sees a minister and mistakes him for the sovereign.
In what appearance does God present Himself to those who make themselves worthy to see Him, in some particular form, in a human figure or as a shining spotlight of light? In human language He cannot be described, because there is no point of comparison for us that can give us an idea of Him. We are like those blind from birth who have been vainly tried to make us understand the brightness of the sun. Our vocabulary is limited to our needs and to the circle of our ideas; that of savages would not serve to describe the wonders of civilisation; that of the more civilised peoples is too poor to describe the splendours of the heavens, and our intelligence is too limited to comprehend them, just as our sight, too weak, would be dazzled.