Fortunately, with some homework, you will quite literally find a plethora of references to the doctrine of theosis in the ancient world, including in Judaism and Christianity. Indeed, even Jesus Christ himself declared that man had divine potential when he repeated the Psalm, "ye are gods," to teach the Jews it was not blasphemous for him to call himself the Son of God (John 10:31-36; cf. Ps. 82:6). Indeed, even the idea of "fallen" man indicates that he was once at a higher state, a state to which he can return through the atonement of Jesus Christ. The Latter-day Saints believe that we are literally children of God, our Father in Heaven, and as His children we have the potential to become just as He is.
Dissertations and books have been written on the subject of theosis, and much more could be said. Suffice it to say, for the present, that even Christianity's most oft-quoted and beloved modern theologian, C. S. Lewis, once said the following:
It is a serious thing to live in a society of possible gods and goddesses, to remember that the dullest and most uninteresting person you talk to may one day be a creature which, if you saw it now, you would be strongly tempted to worship...(The Weight of Glory)
The command "Be ye perfect" is not idealistic gas. Nor is it a command to do the impossible. He is going to make us into creatures that can obey that command. He said (in the Bible) that we were "gods" and He is going to make good His words. If we let Him - for we can prevent Him, if we choose - He will make the feeblest and filthiest of us into a god or goddess, dazzling, radiant, immortal creatures, pulsating all through with such energy and joy and wisdom and love as we cannot now imagine, a bright stainless mirror which reflects back to Him perfectly (though, of course, on a smaller scale) His own boundless power and delight and goodness. The process will be long and in parts very painful; but that is what we are in for. Nothing less. He meant what he said. (Mere Christianity)
Morality is indispensable: but the Divine Life, which gives itself to us and which calls us to be gods, intends for us something in which morality will be swallowed up. We are to be remade. . . . we shall find underneath it all a thing we have never yet imagined: a real man, an ageless god, a son of God, strong, radiant, wise, beautiful, and drenched in joy. (The Grand Miracle)
One of my favorite lines in The Lost Symbol on this subject was a simple statement from Peter Solomon:
"A wise man once told me," Peter said, his voice faint now, "the only difference between you and God is that you have forgotten you are divine" (p. 492).
Mormon References
I want to take note of the two references to Mormonism in The Lost Symbol. The first is on page 79:
"As are many equally improbable beliefs." Langdon often reminded his students that most modern religions included stories that did not hold up to scientific scrutiny: everything from Moses parting the Red Sea . . .to Joseph Smith using magic eyeglasses to translate the Book of Mormon from a series of gold plates he found buried in upstate New York. Wide acceptance of an idea is not proof of its validity (p. 79).
This is somewhat of a backhanded compliment. On the one hand, Langdon is saying that the stated origins of the Book of Mormon are improbable based on scientific scrutiny. On the other hand, he compares the belief to Moses parting the Red Sea, quite a miracle and one that many millions of several different faiths believe was a literal reality.
What is interesting is that even though the stated origins of the Book of Mormon may not hold up to "scientific" scrutiny (and they probably never will), neither has science, or anyone else, been able to determine and explain the supposed actual origins of the complex book of 588 printed pages, produced in 60 some-odd working days, if it wasn't translated as it claims. It is like Dan Brown producing The Lost Symbol in sixty days, instead of six years, and that's giving him extra time with seventy-nine less pages to write. Furthermore, there are references later in The Lost Symbol that indicate that the always-incredulous Langdon might have began to think differently after his experiences. Warren Bellamy teaches him:
"I've learned never to close my mind to an idea simply because it seems miraculous" (p. 211).
The other reference to Mormonism is on page 438: