How is soul defined? Who possesses souls? Do all animal possess souls? How about microscopic organisms? How about an ant? A cocroach, a bee, a flea, a worm? If only humans possess soul how do you explain the population growth? Lot of times religion is only a way to pacify the mind that there is a reason for all this and not just some meaningless chance. A meaningless chance when two people met because one decided to wait for the next bus or something of that sort. They make love on different days, if the union had been on tuesday, the child would have been someone else. If the sexual union was on some other day then the child would be someone else.
Nobody wants to believe that they are not part of a grand design supervised by the great one himself. I mean why would they, they grow up in a social cocoon. Their vision gets marred by manmade institutions of marriage, love, and meaningful existence. Step back few hundred thousand years ago when the first homo sapiens existed. They were only animals needing food and shelter. The sun the all powerful entity was their god because it was inexplicable. They developed language and some smart ones decided to rule over the less smart ones by pretending to have knowledge of the bigger meaning in life. These were the first priests that ruled the homo sapiens.