I think it facile to claim, as some people do, that a rather amorphous, mostly unconnected group of people--in this case, the so-called New Age "movement"--has any conniving strategy to take over an established religion (Christianity). It is instead a "Christian-spiritualist" idea to attribute to an unorganized group of people a reification which is not there. It is a trait of the human mind to find meaning, such as finding faces in clouds. Humans are, after all, what I call Homo habilis sententia--Man, Meaning-Maker (admittedly a rather clumsy label). Others describe the phenomenon as "hypertrophy of social cognition"--seeing intention, direction, purpose, even when there is none. I would say "New Agers" believe that any spiritual development occurs only in the hearts and minds of people. They are a rather passive lot.
To use the words of Alice Bailey and other Theosophists, who were writing in the late 19th and early 20th centuries, is, I believe, looking too far outside the current historical context to an earlier outmoded time. Even Alfred Russel Wallace, a top, medaled scientist at the time (and not a Theosophist) used language, and believed, in ways we today label racist. Terms such as "primitive races" reflected the thinking of the time and would have been used in Christian pulpits throughout North America and Europe. The evolutionist-primitive/superior races language was written in every school textbook used in America. Those were the beliefs at that time and led to the "White Man's burden" program of taking Christianity to the "inferior races." In contrast, the Theosophists seem quite benign.
Anachronistic use today of writings to judge past peoples is invalid historiography. Otherwise, we would have to judge Thomas Jefferson, Abraham Lincoln, and others, in a different light. They were, after all, what we today would understand as individuals terribly bigoted toward African-Americans and Native Americans. But my concern here is the use of history--earlier esoteric writings of a century past--to judge people who today might think of themselves as "New Age." By the same token, it would not be proper to judge Christians today using sermons from yestercentury.