In my universe:
Following the days of humanity’s fall from grace, the human race remained rudderless. Cain killed Abel, Enoch did something right, Noah saved a few people in a gopher wood boat, and Nimrod built a tower to his own glory. The Titans and spirits on the earth were still charged with watching over creation, and the human race was still off limits. It was after Babel that the Gods came into their own, some by violence on their own fathers and mothers, and were given the charge of testing and trying the souls of people and, in a real sense, bearing witness to creation and the Most High God (the One True God) so that no one would have an excuse.
Unfortunately, even in those early days before Babel, the “Sons of God found the daughters of men fair…” All the more so after the tower fell. Spiritual power, the source of the magic, passed into the human race through the children born out of the union of God (or spirit) and mortal. Heracles (Hercules), Achilles and Aneas are three very good examples. Over generations, that blood and power would diminish, but it was one good way in which magic came to people. Merlin, they say, had an incubus for a father.
THE other way magic could come into people was by gift. The Princess, the life of my time traveler born in 228 BC was gifted by Artemis to hunt and track and was considered the best archer in her generation. The fact that she used her skills to hunt and track down certain men is a bit of a story, but the power she had came by way of a gift, and it was found over time that such gifts often, though not always, also passed down through the generations, always diminishing, until disappearing in the general population
Even the littlest spirits could gift people in small ways. Think of the three fairies who spoke blessings over the cradle of sleeping beauty.
Now, in all cases, the gift or blood would eventually breed out over the generations, unless people of magic married only those who also had magic. This occurred in my stories of the Other Earth. It is the place where many people, in particular people of magic went when the great persecutions came with the rise of the last and greatest of the ancient empires (and their collapse into dark ages) and the rise of the world’s great religions. Of course, when a small population inbreeds, there are other dangers, like a very powerful wizard with the mind of an idiot… but that is another story.
On our earth, in our day, there isn’t much magic left – though I won’t say there is none. Even though when Christ came the whole configuration of spiritual life, the source of the magic on earth changed. The Gods gave up their little bit of flesh and blood and “went over to the other side.” Most of the greater and lesser spirits did this also, and though their spiritual forces, the spirits of the Gods, still function on the earth, they are once again deaf, dumb and blind.
Into this place, the Most High (God, himself) has come to “gift” people, his own Holy Spirit coming upon them to do, not what we call magic, but miracles. At the same time, the angels of God are able to empower and defend his people, and good thing, because the demons are presently able to both empower some for use and attack many. Steal, kill and destroy is what demons do best, but wickedness in magic will have to wait for the next post.