It's not until they reach the 30th degree that they begin to understand what it's really about and even then, if they are blinkered enough, they will still carry on believing that Freemasonry is a good wholesome Christian fraternity but if you read my post, you'll have discovered that many, many eminent Freemasons have gone on to form occult societies, like Dr. William Wynn Westcott, S.L. MacGregor Mathers, Gerald Gardner and Alex Sanders, for example.
This is what witches Janet and Stewart Farrar say about Freemasonry:
"It is generally agreed that the biggest single influence in the modern expansion of ritual magic and the occult explosion in general, in the Western world, was the Golden Dawn. This magical fraternity, founded by Freemasons at the end of the 19th century, developed a complex ritual system with ten degrees of initiation relating to the Cabalistic Sephiroth." (Janet and Stewart Farrar, "The Life and Times of A Modern Witch", Phoenix Publishing Company, p. 121)