I'd tend to agree that nobody knows for certainty all truths of the universe, but there are well-documented processes like insight meditation that lead to certain altered states of consciousness (jhanas/dhyana & samadhi), that some people call knowledge/experience of the Soul or God. While you might disagree with the interpretation of these experiences as the 'Soul' 'God', the experiences are concrete enough to light up the brain in a brain scan.
> I do think that all popular religions on earth were created by people, though.
They were, but they were based on people who had real experiences of god or the spirit or what have you. Swami Vivekananda said it better than I can in Raja Yoga (1896):
> Religion, as it is generally taught all over the world, is said to be based upon faith and belief, and, in most cases, consists only of different sets of theories, and that is the reason why we find all religions quarrelling with one another. These theories, again, are based upon belief. One man says there is a great Being sitting above the clouds and governing the whole universe, and he asks me to believe that solely on the authority of his assertion. In the same way, I may have my own ideas, which I am asking others to believe, and if they ask a reason, I cannot give them any. This is why religion and metaphysical philosophy have a bad name nowadays. Every educated man seems to say, "Oh, these religions are only bundles of theories without any standard to judge them by, each man preaching his own pet ideas." Nevertheless, there is a basis of universal belief in religion, governing all the different theories and all the varying ideas of different sects in different countries. Going to their basis we find that they also are based upon universal experiences. [...]
> The teachers of the science of Yoga, therefore, declare that religion is not only based upon the experience of ancient times, but that no man can be religious until he has the same perceptions himself. Yoga is the science which teaches us how to get these perceptions. It is not much use to talk about religion until one has felt it. Why is there so much disturbance, so much fighting and quarrelling in the name of God? There has been more bloodshed in the name of God than for any other cause, because people never went to the fountain-head; they were content only to give a mental assent to the customs of their forefathers, and wanted others to do the same. What right has a man to say he has a soul if he does not feel it, or that there is a God if he does not see Him? If there is a God we must see Him, if there is a soul we must perceive it; otherwise it is better not to believe. It is better to be an outspoken atheist than a hypocrite. The modern idea, on the one hand, with the "learned" is that religion and metaphysics and all search after a Supreme Being are futile; on the other hand, with the semi-educated, the idea seems to be that these things really have no basis; their only value consists in the fact that they furnish strong motive powers for doing good to the world. If men believe in a God, they may become good, and moral, and so make good citizens. We cannot blame them for holding such ideas, seeing that all the teaching these men get is simply to believe in an eternal rigmarole of words, without any substance behind them.