"The Master Key is here given to the world as a means of tapping the great Cosmic Intelligence and attracting from it that which corresponds to the ambitions, and aspirations, of each reader."
In the above sentence, I don't understand why there are 2 relative pronouns (that which) are used one after another. What is the function of this structure? And can I simply use 'that' or 'which' in that position (i.e. just use 1 relative pronoun)?